diff --git a/.gitignore b/.gitignore
index 3dde301c..d85bf2d3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -15,3 +15,4 @@ build/
 *.iml
 *.jks
 keystore.properties
+package-info.java
diff --git a/.idea/codeStyles/Project.xml b/.idea/codeStyles/Project.xml
index 56aadf89..b9a1bf45 100644
--- a/.idea/codeStyles/Project.xml
+++ b/.idea/codeStyles/Project.xml
@@ -94,6 +94,8 @@
       <option name="XML_LEGACY_SETTINGS_IMPORTED" value="true" />
     </XML>
     <codeStyleSettings language="JAVA">
+      <option name="METHOD_ANNOTATION_WRAP" value="0" />
+      <option name="FIELD_ANNOTATION_WRAP" value="0" />
       <arrangement>
         <groups />
         <rules>
diff --git a/app/build.gradle b/app/build.gradle
index b0bcc3b6..f63726d3 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -1,4 +1,5 @@
 apply plugin: 'com.android.application'
+apply from: 'nonnull.gradle'
 
 // Create a variable called keystorePropertiesFile, and initialize it to your
 // keystore.properties file, in the rootProject folder.
@@ -56,6 +57,7 @@ ext {
     databindingVersion = '3.1.3'
     supportLibsVersion = '27.1.1'
     streamsupportVersion = '1.6.0'
+    jsr305Version = '3.0.2'
 }
 
 dependencies {
@@ -67,6 +69,7 @@ dependencies {
     implementation "com.android.support:support-annotations:$supportLibsVersion"
     implementation "net.sourceforge.streamsupport:android-retrofuture:$streamsupportVersion"
     implementation "net.sourceforge.streamsupport:android-retrostreams:$streamsupportVersion"
+    implementation "com.google.code.findbugs:jsr305:$jsr305Version"
 }
 
 tasks.withType(JavaCompile) {
diff --git a/app/nonnull.gradle b/app/nonnull.gradle
new file mode 100644
index 00000000..014e999a
--- /dev/null
+++ b/app/nonnull.gradle
@@ -0,0 +1,87 @@
+/*
+ * Copyright © 2018 Eric Kuck <eric@bluelinelabs.com>.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+task generateNonNullJavaFiles(dependsOn: "assembleDebug", type: Copy) {
+    group = "Copying"
+    description = "Generate package-info.java classes"
+
+    def basePackage = "com" + File.separatorChar + "wireguard"
+    def mainSrcPhrase = "src" + File.separatorChar + "main" + File.separatorChar +
+            "java" + File.separatorChar
+    def mainTestSrcPhrase = "src" + File.separatorChar + "test" + File.separatorChar +
+            "java" + File.separatorChar
+    def mainAndroidTestSrcPhrase = "src" + File.separatorChar + "androidTest" + File.separatorChar +
+            "java" + File.separatorChar
+
+    def sourceDir = file( "${projectDir}" + File.separatorChar + "src" + File.separatorChar +
+            "main" + File.separatorChar + "java" + File.separatorChar +
+            basePackage )
+    def testSourceDir = file( "${projectDir}" + File.separatorChar + "src" + File.separatorChar +
+            "test" + File.separatorChar + "java" + File.separatorChar +
+            basePackage)
+    def androidTestSourceDir = file( "${projectDir}" + File.separatorChar + "src" + File
+            .separatorChar +
+            "androidTest" + File.separatorChar + "java" + File.separatorChar +
+            basePackage )
+
+    generateInfoFiles(sourceDir, mainSrcPhrase);
+    sourceDir.eachDirRecurse { dir ->
+        generateInfoFiles(dir, mainSrcPhrase)
+    }
+    if (file(testSourceDir).exists()) {
+        generateInfoFiles(testSourceDir, mainTestSrcPhrase);
+        testSourceDir.eachDirRecurse { dir ->
+            generateInfoFiles(dir, mainTestSrcPhrase)
+        }
+    }
+    if (file(androidTestSourceDir).exists()) {
+        generateInfoFiles(androidTestSourceDir, mainAndroidTestSrcPhrase);
+        androidTestSourceDir.eachDirRecurse { dir ->
+            generateInfoFiles(dir, mainAndroidTestSrcPhrase)
+        }
+    }
+    println "[SUCCESS] NonNull generator: package-info.java files checked"
+}
+
+private void generateInfoFiles(File dir, String mainSrcPhrase) {
+    def infoFileContentHeader = getFileContentHeader();
+    def infoFileContentFooter = getFileContentFooter();
+    def infoFilePath = dir.getAbsolutePath() + File.separatorChar + "package-info.java"
+
+    //file(infoFilePath).delete(); //do not use in production code
+    if (!file(infoFilePath).exists()) {
+        def infoFileContentPackage = getFileContentPackage(dir.getAbsolutePath(), mainSrcPhrase);
+        new File(infoFilePath).write(infoFileContentHeader +
+                infoFileContentPackage + infoFileContentFooter)
+        println "[dir] " + infoFilePath + "  created";
+    }
+}
+
+def getFileContentPackage(String path, String mainSrcPhrase) {
+    def mainSrcPhraseIndex = path.indexOf(mainSrcPhrase)
+    def output = path.substring(mainSrcPhraseIndex)
+
+    // Win hotfix
+    if (System.properties['os.name'].toLowerCase().contains('windows')) {
+        output = output.replace("\\", "/")
+        mainSrcPhrase = mainSrcPhrase.replace("\\", "/")
+    }
+
+    return "package " + output.replaceAll(mainSrcPhrase, "").replaceAll(
+                "/", ".") + ";\n"
+}
+
+def getFileContentHeader() {
+    return  "/**\n" +
+            " * Make all method parameters @NonNull by default.\n" +
+            " */\n" +
+            "@NonNullForAll\n"
+}
+
+def getFileContentFooter() {
+    return  "\n" +
+            "import com.wireguard.util.NonNullForAll;\n"
+}
+
diff --git a/app/src/main/java/com/wireguard/android/Application.java b/app/src/main/java/com/wireguard/android/Application.java
index f3045831..f4a4290e 100644
--- a/app/src/main/java/com/wireguard/android/Application.java
+++ b/app/src/main/java/com/wireguard/android/Application.java
@@ -10,6 +10,7 @@ import android.os.AsyncTask;
 import android.os.Handler;
 import android.os.Looper;
 import android.preference.PreferenceManager;
+import android.support.annotation.Nullable;
 import android.support.v7.app.AppCompatDelegate;
 
 import com.wireguard.android.backend.Backend;
@@ -26,18 +27,19 @@ import java.io.File;
 import java.lang.ref.WeakReference;
 import java.util.ArrayList;
 import java.util.Collection;
+import java.util.Objects;
 import java.util.concurrent.Executor;
 
 public class Application extends android.app.Application {
-    private static WeakReference<Application> weakSelf;
-    private AsyncWorker asyncWorker;
-    private Backend backend;
-    private RootShell rootShell;
-    private SharedPreferences sharedPreferences;
-    private ToolsInstaller toolsInstaller;
-    private TunnelManager tunnelManager;
-    private Handler handler;
-    private Collection<BackendCallback> haveBackendCallbacks = new ArrayList<>();
+    @SuppressWarnings("NullableProblems") private static WeakReference<Application> weakSelf;
+    @SuppressWarnings("NullableProblems") private AsyncWorker asyncWorker;
+    @SuppressWarnings("NullableProblems") private RootShell rootShell;
+    @SuppressWarnings("NullableProblems") private SharedPreferences sharedPreferences;
+    @SuppressWarnings("NullableProblems") private ToolsInstaller toolsInstaller;
+    @SuppressWarnings("NullableProblems") private TunnelManager tunnelManager;
+    @SuppressWarnings("NullableProblems") private Handler handler;
+    @Nullable private Backend backend;
+    @Nullable private Collection<BackendCallback> haveBackendCallbacks = new ArrayList<>();
     private final Object haveBackendCallbacksLock = new Object();
 
     public Application() {
@@ -65,9 +67,11 @@ public class Application extends android.app.Application {
                 if (app.backend == null)
                     app.backend = new GoBackend(app.getApplicationContext());
                 synchronized (app.haveBackendCallbacksLock) {
-                    for (final BackendCallback callback : app.haveBackendCallbacks)
-                        app.handler.post(() -> callback.callback(app.backend));
-                    app.haveBackendCallbacks = null;
+                    if (app.haveBackendCallbacks != null) {
+                        for (final BackendCallback callback : app.haveBackendCallbacks)
+                            app.handler.post(() -> callback.callback(app.backend));
+                        app.haveBackendCallbacks = null;
+                    }
                 }
             }
             return app.backend;
@@ -82,10 +86,12 @@ public class Application extends android.app.Application {
     public static void onHaveBackend(final BackendCallback callback) {
         final Application app = get();
         synchronized (app.haveBackendCallbacksLock) {
-            if (app.haveBackendCallbacks == null)
+            if (app.haveBackendCallbacks == null) {
+                Objects.requireNonNull(app.backend, "Backend still null in onHaveBackend call");
                 callback.callback(app.backend);
-            else
+            } else {
                 app.haveBackendCallbacks.add(callback);
+            }
         }
     }
 
diff --git a/app/src/main/java/com/wireguard/android/QuickTileService.java b/app/src/main/java/com/wireguard/android/QuickTileService.java
index 77f01502..008fdee8 100644
--- a/app/src/main/java/com/wireguard/android/QuickTileService.java
+++ b/app/src/main/java/com/wireguard/android/QuickTileService.java
@@ -12,12 +12,11 @@ import android.databinding.Observable;
 import android.databinding.Observable.OnPropertyChangedCallback;
 import android.graphics.Bitmap;
 import android.graphics.Canvas;
-import android.graphics.drawable.BitmapDrawable;
-import android.graphics.drawable.Drawable;
 import android.graphics.drawable.Icon;
 import android.os.Build;
 import android.service.quicksettings.Tile;
 import android.service.quicksettings.TileService;
+import android.support.annotation.Nullable;
 import android.util.Log;
 import android.widget.Toast;
 
@@ -41,9 +40,9 @@ public class QuickTileService extends TileService {
 
     private final OnStateChangedCallback onStateChangedCallback = new OnStateChangedCallback();
     private final OnTunnelChangedCallback onTunnelChangedCallback = new OnTunnelChangedCallback();
-    private Tunnel tunnel;
-    private Icon iconOn;
-    private Icon iconOff;
+    @Nullable private Tunnel tunnel;
+    @Nullable private Icon iconOn;
+    @Nullable private Icon iconOff;
 
     @SuppressWarnings("deprecation")
     @Override
@@ -91,7 +90,7 @@ public class QuickTileService extends TileService {
     }
 
     private void onToggleFinished(@SuppressWarnings("unused") final State state,
-                                  final Throwable throwable) {
+                                  @Nullable final Throwable throwable) {
         if (throwable == null)
             return;
         final String error = ExceptionLoggers.unwrapMessage(throwable);
diff --git a/app/src/main/java/com/wireguard/android/activity/BaseActivity.java b/app/src/main/java/com/wireguard/android/activity/BaseActivity.java
index 9b535d79..51357d89 100644
--- a/app/src/main/java/com/wireguard/android/activity/BaseActivity.java
+++ b/app/src/main/java/com/wireguard/android/activity/BaseActivity.java
@@ -9,6 +9,7 @@ package com.wireguard.android.activity;
 import android.databinding.CallbackRegistry;
 import android.databinding.CallbackRegistry.NotifierCallback;
 import android.os.Bundle;
+import android.support.annotation.Nullable;
 
 import com.wireguard.android.Application;
 import com.wireguard.android.model.Tunnel;
@@ -24,19 +25,19 @@ public abstract class BaseActivity extends ThemeChangeAwareActivity {
     private static final String KEY_SELECTED_TUNNEL = "selected_tunnel";
 
     private final SelectionChangeRegistry selectionChangeRegistry = new SelectionChangeRegistry();
-    private Tunnel selectedTunnel;
+    @Nullable private Tunnel selectedTunnel;
 
-    public void addOnSelectedTunnelChangedListener(
-            final OnSelectedTunnelChangedListener listener) {
+    public void addOnSelectedTunnelChangedListener(final OnSelectedTunnelChangedListener listener) {
         selectionChangeRegistry.add(listener);
     }
 
+    @Nullable
     public Tunnel getSelectedTunnel() {
         return selectedTunnel;
     }
 
     @Override
-    protected void onCreate(final Bundle savedInstanceState) {
+    protected void onCreate(@Nullable final Bundle savedInstanceState) {
         // Restore the saved tunnel if there is one; otherwise grab it from the arguments.
         String savedTunnelName = null;
         if (savedInstanceState != null)
@@ -59,14 +60,14 @@ public abstract class BaseActivity extends ThemeChangeAwareActivity {
         super.onSaveInstanceState(outState);
     }
 
-    protected abstract void onSelectedTunnelChanged(Tunnel oldTunnel, Tunnel newTunnel);
+    protected abstract void onSelectedTunnelChanged(@Nullable Tunnel oldTunnel, @Nullable Tunnel newTunnel);
 
     public void removeOnSelectedTunnelChangedListener(
             final OnSelectedTunnelChangedListener listener) {
         selectionChangeRegistry.remove(listener);
     }
 
-    public void setSelectedTunnel(final Tunnel tunnel) {
+    public void setSelectedTunnel(@Nullable final Tunnel tunnel) {
         final Tunnel oldTunnel = selectedTunnel;
         if (Objects.equals(oldTunnel, tunnel))
             return;
@@ -76,7 +77,7 @@ public abstract class BaseActivity extends ThemeChangeAwareActivity {
     }
 
     public interface OnSelectedTunnelChangedListener {
-        void onSelectedTunnelChanged(Tunnel oldTunnel, Tunnel newTunnel);
+        void onSelectedTunnelChanged(@Nullable Tunnel oldTunnel, @Nullable Tunnel newTunnel);
     }
 
     private static final class SelectionChangeNotifier
diff --git a/app/src/main/java/com/wireguard/android/activity/MainActivity.java b/app/src/main/java/com/wireguard/android/activity/MainActivity.java
index e7f438f2..5a8134f3 100644
--- a/app/src/main/java/com/wireguard/android/activity/MainActivity.java
+++ b/app/src/main/java/com/wireguard/android/activity/MainActivity.java
@@ -9,6 +9,7 @@ package com.wireguard.android.activity;
 import android.annotation.SuppressLint;
 import android.content.Intent;
 import android.os.Bundle;
+import android.support.annotation.Nullable;
 import android.support.v4.app.Fragment;
 import android.support.v4.app.FragmentManager;
 import android.support.v4.app.FragmentTransaction;
@@ -22,6 +23,8 @@ import com.wireguard.android.fragment.TunnelEditorFragment;
 import com.wireguard.android.fragment.TunnelListFragment;
 import com.wireguard.android.model.Tunnel;
 
+import java.util.List;
+
 import java9.util.stream.Stream;
 
 /**
@@ -33,6 +36,7 @@ import java9.util.stream.Stream;
 public class MainActivity extends BaseActivity {
     private static final String KEY_STATE = "fragment_state";
     private static final String TAG = "WireGuard/" + MainActivity.class.getSimpleName();
+
     private State state = State.EMPTY;
 
     private boolean moveToState(final State nextState) {
@@ -70,13 +74,19 @@ public class MainActivity extends BaseActivity {
 
     @Override
     public void onBackPressed() {
-        TunnelListFragment fragment = null;
-        try {
-            fragment = ((TunnelListFragment) getSupportFragmentManager().getFragments().get(0));
-        } catch (final ClassCastException ignored) { }
-        if (fragment == null || !fragment.collapseActionMenu()) {
-            if (!moveToState(State.ofLayer(state.layer - 1)))
-                super.onBackPressed();
+        final List<Fragment> fragments = getSupportFragmentManager().getFragments();
+
+        boolean handled = false;
+        if (!fragments.isEmpty() && fragments.get(0) instanceof TunnelListFragment) {
+            handled = ((TunnelListFragment) fragments.get(0)).collapseActionMenu();
+        }
+
+        if (!handled) {
+            handled = moveToState(State.ofLayer(state.layer - 1));
+        }
+
+        if (!handled) {
+            super.onBackPressed();
         }
     }
 
@@ -84,7 +94,7 @@ public class MainActivity extends BaseActivity {
     // calling View#performClick defeats the purpose of it.
     @SuppressLint("ClickableViewAccessibility")
     @Override
-    protected void onCreate(final Bundle savedInstanceState) {
+    protected void onCreate(@Nullable final Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.main_activity);
         if (savedInstanceState != null && savedInstanceState.getString(KEY_STATE) != null)
@@ -99,9 +109,10 @@ public class MainActivity extends BaseActivity {
         final int actionBarId = getResources().getIdentifier("action_bar", "id", getPackageName());
         if (actionBarId != 0 && findViewById(actionBarId) != null) {
             findViewById(actionBarId).setOnTouchListener((v, e) -> {
-                try {
-                    ((TunnelListFragment) getSupportFragmentManager().getFragments().get(0)).collapseActionMenu();
-                } catch (final ClassCastException ignored) { }
+                final List<Fragment> fragments = getSupportFragmentManager().getFragments();
+                if (!fragments.isEmpty() && fragments.get(0) instanceof TunnelListFragment) {
+                    ((TunnelListFragment) fragments.get(0)).collapseActionMenu();
+                }
                 return false;
             });
         }
@@ -142,7 +153,7 @@ public class MainActivity extends BaseActivity {
     }
 
     @Override
-    protected void onSelectedTunnelChanged(final Tunnel oldTunnel, final Tunnel newTunnel) {
+    protected void onSelectedTunnelChanged(@Nullable final Tunnel oldTunnel, @Nullable final Tunnel newTunnel) {
         moveToState(newTunnel != null ? State.DETAIL : State.LIST);
     }
 
@@ -157,10 +168,10 @@ public class MainActivity extends BaseActivity {
         DETAIL(TunnelDetailFragment.class, 2),
         EDITOR(TunnelEditorFragment.class, 3);
 
-        private final String fragment;
+        @Nullable private final String fragment;
         private final int layer;
 
-        State(final Class<? extends Fragment> fragment, final int layer) {
+        State(@Nullable final Class<? extends Fragment> fragment, final int layer) {
             this.fragment = fragment != null ? fragment.getName() : null;
             this.layer = layer;
         }
diff --git a/app/src/main/java/com/wireguard/android/activity/SettingsActivity.java b/app/src/main/java/com/wireguard/android/activity/SettingsActivity.java
index ed2da4dc..066d377f 100644
--- a/app/src/main/java/com/wireguard/android/activity/SettingsActivity.java
+++ b/app/src/main/java/com/wireguard/android/activity/SettingsActivity.java
@@ -8,12 +8,13 @@ package com.wireguard.android.activity;
 
 import android.content.pm.PackageManager;
 import android.os.Bundle;
-import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v4.app.ActivityCompat;
 import android.support.v4.content.ContextCompat;
 import android.support.v7.preference.Preference;
 import android.support.v7.preference.PreferenceFragmentCompat;
 import android.support.v7.preference.PreferenceScreen;
+import android.util.SparseArray;
 import android.view.MenuItem;
 
 import com.wireguard.android.Application;
@@ -22,16 +23,14 @@ import com.wireguard.android.backend.WgQuickBackend;
 
 import java.util.ArrayList;
 import java.util.Arrays;
-import java.util.HashMap;
 import java.util.List;
-import java.util.Map;
 
 /**
  * Interface for changing application-global persistent settings.
  */
 
 public class SettingsActivity extends ThemeChangeAwareActivity {
-    private final Map<Integer, PermissionRequestCallback> permissionRequestCallbacks = new HashMap<>();
+    private final SparseArray<PermissionRequestCallback> permissionRequestCallbacks = new SparseArray<>();
     private int permissionRequestCounter;
 
     public void ensurePermissions(final String[] permissions, final PermissionRequestCallback cb) {
@@ -54,7 +53,7 @@ public class SettingsActivity extends ThemeChangeAwareActivity {
     }
 
     @Override
-    protected void onCreate(final Bundle savedInstanceState) {
+    protected void onCreate(@Nullable final Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         if (getSupportFragmentManager().findFragmentById(android.R.id.content) == null) {
             getSupportFragmentManager().beginTransaction()
@@ -76,8 +75,8 @@ public class SettingsActivity extends ThemeChangeAwareActivity {
 
     @Override
     public void onRequestPermissionsResult(final int requestCode,
-                                           @NonNull final String[] permissions,
-                                           @NonNull final int[] grantResults) {
+                                           final String[] permissions,
+                                           final int[] grantResults) {
         final PermissionRequestCallback f = permissionRequestCallbacks.get(requestCode);
         if (f != null) {
             permissionRequestCallbacks.remove(requestCode);
diff --git a/app/src/main/java/com/wireguard/android/activity/ThemeChangeAwareActivity.java b/app/src/main/java/com/wireguard/android/activity/ThemeChangeAwareActivity.java
index be61f256..d85a0170 100644
--- a/app/src/main/java/com/wireguard/android/activity/ThemeChangeAwareActivity.java
+++ b/app/src/main/java/com/wireguard/android/activity/ThemeChangeAwareActivity.java
@@ -8,6 +8,7 @@ package com.wireguard.android.activity;
 import android.content.SharedPreferences;
 import android.content.res.Resources;
 import android.os.Bundle;
+import android.support.annotation.Nullable;
 import android.support.v7.app.AppCompatActivity;
 import android.support.v7.app.AppCompatDelegate;
 import android.util.Log;
@@ -19,7 +20,7 @@ import java.lang.reflect.Field;
 public abstract class ThemeChangeAwareActivity extends AppCompatActivity implements SharedPreferences.OnSharedPreferenceChangeListener {
     private static final String TAG = "WireGuard/" + ThemeChangeAwareActivity.class.getSimpleName();
 
-    private static Resources lastResources;
+    @Nullable private static Resources lastResources;
     private static boolean lastDarkMode;
     private static synchronized void invalidateDrawableCache(final Resources resources, final boolean darkMode) {
         if (resources == lastResources && darkMode == lastDarkMode)
@@ -51,7 +52,7 @@ public abstract class ThemeChangeAwareActivity extends AppCompatActivity impleme
 
 
     @Override
-    protected void onCreate(final Bundle savedInstanceState) {
+    protected void onCreate(@Nullable final Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         Application.getSharedPreferences().registerOnSharedPreferenceChangeListener(this);
     }
diff --git a/app/src/main/java/com/wireguard/android/activity/TunnelCreatorActivity.java b/app/src/main/java/com/wireguard/android/activity/TunnelCreatorActivity.java
index 044548ce..99bb4141 100644
--- a/app/src/main/java/com/wireguard/android/activity/TunnelCreatorActivity.java
+++ b/app/src/main/java/com/wireguard/android/activity/TunnelCreatorActivity.java
@@ -7,6 +7,7 @@
 package com.wireguard.android.activity;
 
 import android.os.Bundle;
+import android.support.annotation.Nullable;
 
 import com.wireguard.android.fragment.TunnelEditorFragment;
 import com.wireguard.android.model.Tunnel;
@@ -18,7 +19,7 @@ import com.wireguard.android.model.Tunnel;
 public class TunnelCreatorActivity extends BaseActivity {
     @Override
     @SuppressWarnings("UnnecessaryFullyQualifiedName")
-    protected void onCreate(final Bundle savedInstanceState) {
+    protected void onCreate(@Nullable final Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         if (getSupportFragmentManager().findFragmentById(android.R.id.content) == null) {
             getSupportFragmentManager().beginTransaction()
@@ -28,7 +29,7 @@ public class TunnelCreatorActivity extends BaseActivity {
     }
 
     @Override
-    protected void onSelectedTunnelChanged(final Tunnel oldTunnel, final Tunnel newTunnel) {
+    protected void onSelectedTunnelChanged(@Nullable final Tunnel oldTunnel, @Nullable final Tunnel newTunnel) {
         finish();
     }
 }
diff --git a/app/src/main/java/com/wireguard/android/backend/GoBackend.java b/app/src/main/java/com/wireguard/android/backend/GoBackend.java
index 66d3698f..a075913f 100644
--- a/app/src/main/java/com/wireguard/android/backend/GoBackend.java
+++ b/app/src/main/java/com/wireguard/android/backend/GoBackend.java
@@ -10,6 +10,7 @@ import android.app.PendingIntent;
 import android.content.Context;
 import android.content.Intent;
 import android.os.ParcelFileDescriptor;
+import android.support.annotation.Nullable;
 import android.support.v4.util.ArraySet;
 import android.util.Log;
 
@@ -29,6 +30,7 @@ import com.wireguard.crypto.KeyEncoding;
 import java.net.InetAddress;
 import java.util.Collections;
 import java.util.Formatter;
+import java.util.Objects;
 import java.util.Set;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
@@ -40,7 +42,7 @@ public final class GoBackend implements Backend {
     private static CompletableFuture<VpnService> vpnService = new CompletableFuture<>();
 
     private final Context context;
-    private Tunnel currentTunnel;
+    @Nullable private Tunnel currentTunnel;
     private int currentTunnelHandle = -1;
 
     public GoBackend(final Context context) {
@@ -114,12 +116,14 @@ public final class GoBackend implements Backend {
         return getState(tunnel);
     }
 
-    private void setStateInternal(final Tunnel tunnel, final Config config, final State state)
+    private void setStateInternal(final Tunnel tunnel, @Nullable final Config config, final State state)
             throws Exception {
 
         if (state == State.UP) {
             Log.i(TAG, "Bringing tunnel up");
 
+            Objects.requireNonNull(config, "Trying to bring up a tunnel with no config");
+
             if (VpnService.prepare(context) != null)
                 throw new Exception("VPN service not authorized by user");
 
@@ -245,7 +249,7 @@ public final class GoBackend implements Backend {
         }
 
         @Override
-        public int onStartCommand(final Intent intent, final int flags, final int startId) {
+        public int onStartCommand(@Nullable final Intent intent, final int flags, final int startId) {
             vpnService.complete(this);
             if (intent == null || intent.getComponent() == null || !intent.getComponent().getPackageName().equals(getPackageName())) {
                 Log.d(TAG, "Service started by Always-on VPN feature");
diff --git a/app/src/main/java/com/wireguard/android/backend/WgQuickBackend.java b/app/src/main/java/com/wireguard/android/backend/WgQuickBackend.java
index fbc43dc0..25634841 100644
--- a/app/src/main/java/com/wireguard/android/backend/WgQuickBackend.java
+++ b/app/src/main/java/com/wireguard/android/backend/WgQuickBackend.java
@@ -7,6 +7,7 @@
 package com.wireguard.android.backend;
 
 import android.content.Context;
+import android.support.annotation.Nullable;
 import android.util.Log;
 
 import com.wireguard.android.Application;
@@ -21,6 +22,7 @@ import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Objects;
 import java.util.Set;
 
 import java9.util.stream.Collectors;
@@ -106,8 +108,9 @@ public final class WgQuickBackend implements Backend {
         return getState(tunnel);
     }
 
-    private void setStateInternal(final Tunnel tunnel, final Config config, final State state)
-            throws Exception {
+    private void setStateInternal(final Tunnel tunnel, @Nullable final Config config, final State state) throws Exception {
+        Objects.requireNonNull(config, "Trying to set state with a null config");
+
         final File tempFile = new File(localTemporaryDir, tunnel.getName() + ".conf");
         try (final FileOutputStream stream = new FileOutputStream(tempFile, false)) {
             stream.write(config.toString().getBytes(StandardCharsets.UTF_8));
diff --git a/app/src/main/java/com/wireguard/android/databinding/ItemChangeListener.java b/app/src/main/java/com/wireguard/android/databinding/ItemChangeListener.java
index 0a87d491..909adddc 100644
--- a/app/src/main/java/com/wireguard/android/databinding/ItemChangeListener.java
+++ b/app/src/main/java/com/wireguard/android/databinding/ItemChangeListener.java
@@ -9,6 +9,7 @@ package com.wireguard.android.databinding;
 import android.databinding.DataBindingUtil;
 import android.databinding.ObservableList;
 import android.databinding.ViewDataBinding;
+import android.support.annotation.Nullable;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
@@ -16,6 +17,7 @@ import android.view.ViewGroup;
 import com.wireguard.android.BR;
 
 import java.lang.ref.WeakReference;
+import java.util.Objects;
 
 /**
  * Helper class for binding an ObservableList to the children of a ViewGroup.
@@ -26,7 +28,7 @@ class ItemChangeListener<T> {
     private final ViewGroup container;
     private final int layoutId;
     private final LayoutInflater layoutInflater;
-    private ObservableList<T> list;
+    @Nullable private ObservableList<T> list;
 
     ItemChangeListener(final ViewGroup container, final int layoutId) {
         this.container = container;
@@ -34,17 +36,21 @@ class ItemChangeListener<T> {
         layoutInflater = LayoutInflater.from(container.getContext());
     }
 
-    private View getView(final int position, final View convertView) {
-        ViewDataBinding binding = DataBindingUtil.getBinding(convertView);
-        if (binding == null)
+    private View getView(final int position, @Nullable final View convertView) {
+        ViewDataBinding binding = convertView != null ? DataBindingUtil.getBinding(convertView) : null;
+        if (binding == null) {
             binding = DataBindingUtil.inflate(layoutInflater, layoutId, container, false);
+        }
+
+        Objects.requireNonNull(list, "Trying to get a view while list is still null");
+
         binding.setVariable(BR.collection, list);
         binding.setVariable(BR.item, list.get(position));
         binding.executePendingBindings();
         return binding.getRoot();
     }
 
-    void setList(final ObservableList<T> newList) {
+    void setList(@Nullable final ObservableList<T> newList) {
         if (list != null)
             list.removeOnListChangedCallback(callback);
         list = newList;
diff --git a/app/src/main/java/com/wireguard/android/databinding/ObservableKeyedRecyclerViewAdapter.java b/app/src/main/java/com/wireguard/android/databinding/ObservableKeyedRecyclerViewAdapter.java
index d45e60a5..835a3dc4 100644
--- a/app/src/main/java/com/wireguard/android/databinding/ObservableKeyedRecyclerViewAdapter.java
+++ b/app/src/main/java/com/wireguard/android/databinding/ObservableKeyedRecyclerViewAdapter.java
@@ -10,7 +10,7 @@ import android.content.Context;
 import android.databinding.DataBindingUtil;
 import android.databinding.ObservableList;
 import android.databinding.ViewDataBinding;
-import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v7.widget.RecyclerView;
 import android.support.v7.widget.RecyclerView.Adapter;
 import android.view.LayoutInflater;
@@ -31,8 +31,8 @@ public class ObservableKeyedRecyclerViewAdapter<K, E extends Keyed<? extends K>>
     private final OnListChangedCallback<E> callback = new OnListChangedCallback<>(this);
     private final int layoutId;
     private final LayoutInflater layoutInflater;
-    private ObservableKeyedList<K, E> list;
-    private RowConfigurationHandler rowConfigurationHandler;
+    @Nullable private ObservableKeyedList<K, E> list;
+    @Nullable private RowConfigurationHandler rowConfigurationHandler;
 
     ObservableKeyedRecyclerViewAdapter(final Context context, final int layoutId,
                                        final ObservableKeyedList<K, E> list) {
@@ -46,6 +46,7 @@ public class ObservableKeyedRecyclerViewAdapter<K, E extends Keyed<? extends K>>
         return list != null ? list.size() : 0;
     }
 
+    @Nullable
     private E getItem(final int position) {
         if (list == null || position < 0 || position >= list.size())
             return null;
@@ -58,30 +59,34 @@ public class ObservableKeyedRecyclerViewAdapter<K, E extends Keyed<? extends K>>
         return key != null ? key.hashCode() : -1;
     }
 
+    @Nullable
     private K getKey(final int position) {
         final E item = getItem(position);
         return item != null ? item.getKey() : null;
     }
 
-    @NonNull @Override
-    public ViewHolder onCreateViewHolder(@NonNull final ViewGroup parent, final int viewType) {
+    @Override
+    public ViewHolder onCreateViewHolder(final ViewGroup parent, final int viewType) {
         return new ViewHolder(DataBindingUtil.inflate(layoutInflater, layoutId, parent, false));
     }
 
     @SuppressWarnings("unchecked")
     @Override
-    public void onBindViewHolder(@NonNull final ViewHolder holder, final int position) {
+    public void onBindViewHolder(final ViewHolder holder, final int position) {
         holder.binding.setVariable(BR.collection, list);
         holder.binding.setVariable(BR.key, getKey(position));
         holder.binding.setVariable(BR.item, getItem(position));
         holder.binding.executePendingBindings();
 
         if (rowConfigurationHandler != null) {
-            rowConfigurationHandler.onConfigureRow(holder.binding, getItem(position), position);
+            E item = getItem(position);
+            if (item != null) {
+                rowConfigurationHandler.onConfigureRow(holder.binding, item, position);
+            }
         }
     }
 
-    void setList(final ObservableKeyedList<K, E> newList) {
+    void setList(@Nullable final ObservableKeyedList<K, E> newList) {
         if (list != null)
             list.removeOnListChangedCallback(callback);
         list = newList;
diff --git a/app/src/main/java/com/wireguard/android/fragment/AppListDialogFragment.java b/app/src/main/java/com/wireguard/android/fragment/AppListDialogFragment.java
index 15571297..50de0c39 100644
--- a/app/src/main/java/com/wireguard/android/fragment/AppListDialogFragment.java
+++ b/app/src/main/java/com/wireguard/android/fragment/AppListDialogFragment.java
@@ -39,7 +39,7 @@ public class AppListDialogFragment extends DialogFragment {
 
     private static final String KEY_EXCLUDED_APPS = "excludedApps";
 
-    private List<String> currentlyExcludedApps;
+    private final List<String> currentlyExcludedApps = Arrays.asList(getArguments().getStringArray(KEY_EXCLUDED_APPS));
     private final ObservableKeyedList<String, ApplicationData> appData = new ObservableKeyedArrayList<>();
 
     public static <T extends Fragment & AppExclusionListener> AppListDialogFragment newInstance(final String[] excludedApps, final T target) {
@@ -51,24 +51,12 @@ public class AppListDialogFragment extends DialogFragment {
         return fragment;
     }
 
-    @Override
-    public void onCreate(@Nullable final Bundle savedInstanceState) {
-        super.onCreate(savedInstanceState);
-
-        currentlyExcludedApps = Arrays.asList(getArguments().getStringArray(KEY_EXCLUDED_APPS));
-    }
-
-    @Override
-    public void onAttach(final Context context) {
-        super.onAttach(context);
-    }
-
     @Override
     public Dialog onCreateDialog(final Bundle savedInstanceState) {
         final AlertDialog.Builder alertDialogBuilder = new AlertDialog.Builder(getActivity());
         alertDialogBuilder.setTitle(R.string.excluded_applications);
 
-        AppListDialogFragmentBinding binding = AppListDialogFragmentBinding.inflate(getActivity().getLayoutInflater(), null, false);
+        final AppListDialogFragmentBinding binding = AppListDialogFragmentBinding.inflate(getActivity().getLayoutInflater(), null, false);
         binding.executePendingBindings();
         alertDialogBuilder.setView(binding.getRoot());
 
diff --git a/app/src/main/java/com/wireguard/android/fragment/BaseFragment.java b/app/src/main/java/com/wireguard/android/fragment/BaseFragment.java
index e1d4c87b..f4c6ea81 100644
--- a/app/src/main/java/com/wireguard/android/fragment/BaseFragment.java
+++ b/app/src/main/java/com/wireguard/android/fragment/BaseFragment.java
@@ -10,7 +10,7 @@ import android.content.Context;
 import android.content.Intent;
 import android.databinding.DataBindingUtil;
 import android.databinding.ViewDataBinding;
-import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.design.widget.Snackbar;
 import android.support.v4.app.Fragment;
 import android.util.Log;
@@ -37,10 +37,11 @@ public abstract class BaseFragment extends Fragment implements OnSelectedTunnelC
     private static final String TAG = "WireGuard/" + BaseFragment.class.getSimpleName();
     private static final int REQUEST_CODE_VPN_PERMISSION = 23491;
 
-    private BaseActivity activity;
-    private Tunnel pendingTunnel;
-    private Boolean pendingTunnelUp;
+    @Nullable private BaseActivity activity;
+    @Nullable private Tunnel pendingTunnel;
+    @Nullable private Boolean pendingTunnelUp;
 
+    @Nullable
     protected Tunnel getSelectedTunnel() {
         return activity != null ? activity.getSelectedTunnel() : null;
     }
@@ -65,7 +66,7 @@ public abstract class BaseFragment extends Fragment implements OnSelectedTunnelC
     }
 
     @Override
-    public void onActivityResult(int requestCode, int resultCode, Intent data) {
+    public void onActivityResult(final int requestCode, final int resultCode, @Nullable final Intent data) {
         super.onActivityResult(requestCode, resultCode, data);
 
         if (requestCode == REQUEST_CODE_VPN_PERMISSION) {
@@ -76,7 +77,7 @@ public abstract class BaseFragment extends Fragment implements OnSelectedTunnelC
         }
     }
 
-    protected void setSelectedTunnel(final Tunnel tunnel) {
+    protected void setSelectedTunnel(@Nullable final Tunnel tunnel) {
         if (activity != null)
             activity.setSelectedTunnel(tunnel);
     }
@@ -106,7 +107,7 @@ public abstract class BaseFragment extends Fragment implements OnSelectedTunnelC
         });
     }
 
-    private void setTunnelStateWithPermissionsResult(@NonNull final Tunnel tunnel, final boolean checked) {
+    private void setTunnelStateWithPermissionsResult(final Tunnel tunnel, final boolean checked) {
         tunnel.setState(State.of(checked)).whenComplete((state, throwable) -> {
             if (throwable == null)
                 return;
diff --git a/app/src/main/java/com/wireguard/android/fragment/TunnelDetailFragment.java b/app/src/main/java/com/wireguard/android/fragment/TunnelDetailFragment.java
index 5c35686f..cb1712fc 100644
--- a/app/src/main/java/com/wireguard/android/fragment/TunnelDetailFragment.java
+++ b/app/src/main/java/com/wireguard/android/fragment/TunnelDetailFragment.java
@@ -7,7 +7,7 @@
 package com.wireguard.android.fragment;
 
 import android.os.Bundle;
-import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.view.LayoutInflater;
 import android.view.Menu;
 import android.view.MenuInflater;
@@ -24,14 +24,16 @@ import com.wireguard.config.Config;
  */
 
 public class TunnelDetailFragment extends BaseFragment {
-    private TunnelDetailFragmentBinding binding;
+    @Nullable private TunnelDetailFragmentBinding binding;
 
     private void onConfigLoaded(final String name, final Config config) {
-        binding.setConfig(new Config.Observable(config, name));
+        if (binding != null) {
+            binding.setConfig(new Config.Observable(config, name));
+        }
     }
 
     @Override
-    public void onCreate(final Bundle savedInstanceState) {
+    public void onCreate(@Nullable final Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setHasOptionsMenu(true);
     }
@@ -42,8 +44,8 @@ public class TunnelDetailFragment extends BaseFragment {
     }
 
     @Override
-    public View onCreateView(@NonNull final LayoutInflater inflater, final ViewGroup container,
-                             final Bundle savedInstanceState) {
+    public View onCreateView(final LayoutInflater inflater, @Nullable final ViewGroup container,
+                             @Nullable final Bundle savedInstanceState) {
         super.onCreateView(inflater, container, savedInstanceState);
         binding = TunnelDetailFragmentBinding.inflate(inflater, container, false);
         binding.executePendingBindings();
@@ -57,7 +59,7 @@ public class TunnelDetailFragment extends BaseFragment {
     }
 
     @Override
-    public void onSelectedTunnelChanged(final Tunnel oldTunnel, final Tunnel newTunnel) {
+    public void onSelectedTunnelChanged(@Nullable final Tunnel oldTunnel, @Nullable final Tunnel newTunnel) {
         if (binding == null)
             return;
         binding.setTunnel(newTunnel);
@@ -68,7 +70,11 @@ public class TunnelDetailFragment extends BaseFragment {
     }
 
     @Override
-    public void onViewStateRestored(final Bundle savedInstanceState) {
+    public void onViewStateRestored(@Nullable final Bundle savedInstanceState) {
+        if (binding == null) {
+            return;
+        }
+
         binding.setFragment(this);
         onSelectedTunnelChanged(null, getSelectedTunnel());
         super.onViewStateRestored(savedInstanceState);
diff --git a/app/src/main/java/com/wireguard/android/fragment/TunnelEditorFragment.java b/app/src/main/java/com/wireguard/android/fragment/TunnelEditorFragment.java
index f6f1483a..a6e315f9 100644
--- a/app/src/main/java/com/wireguard/android/fragment/TunnelEditorFragment.java
+++ b/app/src/main/java/com/wireguard/android/fragment/TunnelEditorFragment.java
@@ -11,7 +11,7 @@ import android.content.Context;
 import android.databinding.Observable;
 import android.databinding.ObservableList;
 import android.os.Bundle;
-import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.design.widget.Snackbar;
 import android.support.v4.app.FragmentManager;
 import android.util.Log;
@@ -37,6 +37,7 @@ import com.wireguard.config.Config;
 import com.wireguard.config.Peer;
 
 import java.util.List;
+import java.util.Objects;
 
 /**
  * Fragment for editing a WireGuard configuration.
@@ -47,15 +48,17 @@ public class TunnelEditorFragment extends BaseFragment implements AppExclusionLi
     private static final String KEY_ORIGINAL_NAME = "original_name";
     private static final String TAG = "WireGuard/" + TunnelEditorFragment.class.getSimpleName();
 
-    private TunnelEditorFragmentBinding binding;
-    private Tunnel tunnel;
+    @Nullable private TunnelEditorFragmentBinding binding;
+    @Nullable private Tunnel tunnel;
 
     private void onConfigLoaded(final String name, final Config config) {
-        binding.setConfig(new Config.Observable(config, name));
+        if (binding != null) {
+            binding.setConfig(new Config.Observable(config, name));
+        }
     }
 
     private void onConfigSaved(final Tunnel savedTunnel,
-                               final Throwable throwable) {
+                               @Nullable final Throwable throwable) {
         final String message;
         if (throwable == null) {
             message = getString(R.string.config_save_success, savedTunnel.getName());
@@ -73,7 +76,7 @@ public class TunnelEditorFragment extends BaseFragment implements AppExclusionLi
     }
 
     @Override
-    public void onCreate(final Bundle savedInstanceState) {
+    public void onCreate(@Nullable final Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setHasOptionsMenu(true);
     }
@@ -124,8 +127,8 @@ public class TunnelEditorFragment extends BaseFragment implements AppExclusionLi
     };
 
     @Override
-    public View onCreateView(@NonNull final LayoutInflater inflater, final ViewGroup container,
-                             final Bundle savedInstanceState) {
+    public View onCreateView(final LayoutInflater inflater, @Nullable final ViewGroup container,
+                             @Nullable final Bundle savedInstanceState) {
         super.onCreateView(inflater, container, savedInstanceState);
         binding = TunnelEditorFragmentBinding.inflate(inflater, container, false);
         binding.addOnPropertyChangedCallback(breakObjectOrientedLayeringHandler);
@@ -197,14 +200,14 @@ public class TunnelEditorFragment extends BaseFragment implements AppExclusionLi
     }
 
     @Override
-    public void onSaveInstanceState(@NonNull final Bundle outState) {
+    public void onSaveInstanceState(final Bundle outState) {
         outState.putParcelable(KEY_LOCAL_CONFIG, binding.getConfig());
         outState.putString(KEY_ORIGINAL_NAME, tunnel == null ? null : tunnel.getName());
         super.onSaveInstanceState(outState);
     }
 
     @Override
-    public void onSelectedTunnelChanged(final Tunnel oldTunnel, final Tunnel newTunnel) {
+    public void onSelectedTunnelChanged(@Nullable final Tunnel oldTunnel, @Nullable final Tunnel newTunnel) {
         tunnel = newTunnel;
         if (binding == null)
             return;
@@ -213,7 +216,7 @@ public class TunnelEditorFragment extends BaseFragment implements AppExclusionLi
             tunnel.getConfigAsync().thenAccept(a -> onConfigLoaded(tunnel.getName(), a));
     }
 
-    private void onTunnelCreated(final Tunnel newTunnel, final Throwable throwable) {
+    private void onTunnelCreated(final Tunnel newTunnel, @Nullable final Throwable throwable) {
         final String message;
         if (throwable == null) {
             tunnel = newTunnel;
@@ -232,7 +235,7 @@ public class TunnelEditorFragment extends BaseFragment implements AppExclusionLi
     }
 
     private void onTunnelRenamed(final Tunnel renamedTunnel, final Config newConfig,
-                                 final Throwable throwable) {
+                                 @Nullable final Throwable throwable) {
         final String message;
         if (throwable == null) {
             message = getString(R.string.tunnel_rename_success, renamedTunnel.getName());
@@ -251,7 +254,11 @@ public class TunnelEditorFragment extends BaseFragment implements AppExclusionLi
     }
 
     @Override
-    public void onViewStateRestored(final Bundle savedInstanceState) {
+    public void onViewStateRestored(@Nullable final Bundle savedInstanceState) {
+        if (binding == null) {
+            return;
+        }
+
         binding.setFragment(this);
 
         if (savedInstanceState == null) {
@@ -271,15 +278,16 @@ public class TunnelEditorFragment extends BaseFragment implements AppExclusionLi
 
     public void onRequestSetExcludedApplications(@SuppressWarnings("unused") final View view) {
         final FragmentManager fragmentManager = getFragmentManager();
-        if (fragmentManager != null) {
+        if (fragmentManager != null && binding != null) {
             final String[] excludedApps = Attribute.stringToList(binding.getConfig().getInterfaceSection().getExcludedApplications());
             final AppListDialogFragment fragment = AppListDialogFragment.newInstance(excludedApps, this);
-            fragment.show(getFragmentManager(), null);
+            fragment.show(fragmentManager, null);
         }
     }
 
     @Override
     public void onExcludedAppsSelected(final List<String> excludedApps) {
+        Objects.requireNonNull(binding, "Tried to set excluded apps while no view was loaded");
         binding.getConfig().getInterfaceSection().setExcludedApplications(Attribute.iterableToString(excludedApps));
     }
 
diff --git a/app/src/main/java/com/wireguard/android/fragment/TunnelListFragment.java b/app/src/main/java/com/wireguard/android/fragment/TunnelListFragment.java
index 5dda6cfe..dd8e1337 100644
--- a/app/src/main/java/com/wireguard/android/fragment/TunnelListFragment.java
+++ b/app/src/main/java/com/wireguard/android/fragment/TunnelListFragment.java
@@ -15,7 +15,6 @@ import android.database.Cursor;
 import android.net.Uri;
 import android.os.Bundle;
 import android.provider.OpenableColumns;
-import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.support.design.widget.Snackbar;
 import android.support.v7.app.AppCompatActivity;
@@ -60,20 +59,20 @@ public class TunnelListFragment extends BaseFragment {
     private static final String TAG = "WireGuard/" + TunnelListFragment.class.getSimpleName();
 
     private final ActionModeListener actionModeListener = new ActionModeListener();
-    private ActionMode actionMode;
-    private TunnelListFragmentBinding binding;
+    @Nullable private ActionMode actionMode;
+    @Nullable private TunnelListFragmentBinding binding;
 
     public boolean collapseActionMenu() {
-        if (binding.createMenu.isExpanded()) {
+        if (binding != null && binding.createMenu.isExpanded()) {
             binding.createMenu.collapse();
             return true;
         }
         return false;
     }
 
-    private void importTunnel(final Uri uri) {
+    private void importTunnel(@Nullable final Uri uri) {
         final Activity activity = getActivity();
-        if (activity == null)
+        if (activity == null || uri == null)
             return;
         final ContentResolver contentResolver = activity.getContentResolver();
 
@@ -165,10 +164,10 @@ public class TunnelListFragment extends BaseFragment {
     }
 
     @Override
-    public void onActivityResult(final int requestCode, final int resultCode, final Intent data) {
+    public void onActivityResult(final int requestCode, final int resultCode, @Nullable final Intent data) {
         switch (requestCode) {
             case REQUEST_IMPORT:
-                if (resultCode == Activity.RESULT_OK)
+                if (resultCode == Activity.RESULT_OK && data != null)
                     importTunnel(data.getData());
                 return;
             default:
@@ -178,8 +177,8 @@ public class TunnelListFragment extends BaseFragment {
 
     @SuppressLint("ClickableViewAccessibility")
     @Override
-    public View onCreateView(@NonNull final LayoutInflater inflater, final ViewGroup container,
-                             final Bundle savedInstanceState) {
+    public View onCreateView(final LayoutInflater inflater, @Nullable final ViewGroup container,
+                             @Nullable final Bundle savedInstanceState) {
         super.onCreateView(inflater, container, savedInstanceState);
         binding = TunnelListFragmentBinding.inflate(inflater, container, false);
 
@@ -216,16 +215,18 @@ public class TunnelListFragment extends BaseFragment {
 
     @Override
     public void onPause() {
-        binding.createMenu.collapse();
+        if (binding != null) {
+            binding.createMenu.collapse();
+        }
         super.onPause();
     }
 
     @Override
-    public void onSelectedTunnelChanged(final Tunnel oldTunnel, final Tunnel newTunnel) {
+    public void onSelectedTunnelChanged(@Nullable final Tunnel oldTunnel, @Nullable final Tunnel newTunnel) {
         // Do nothing.
     }
 
-    private void onTunnelDeletionFinished(final Integer count, final Throwable throwable) {
+    private void onTunnelDeletionFinished(final Integer count, @Nullable final Throwable throwable) {
         final String message;
         if (throwable == null) {
             message = getResources().getQuantityString(R.plurals.delete_success, count, count);
@@ -265,8 +266,13 @@ public class TunnelListFragment extends BaseFragment {
     }
 
     @Override
-    public void onViewStateRestored(final Bundle savedInstanceState) {
+    public void onViewStateRestored(@Nullable final Bundle savedInstanceState) {
         super.onViewStateRestored(savedInstanceState);
+
+        if (binding == null) {
+            return;
+        }
+
         binding.setFragment(this);
         binding.setTunnels(Application.getTunnelManager().getTunnels());
         binding.setRowConfigurationHandler((ObservableKeyedRecyclerViewAdapter.RowConfigurationHandler<TunnelListItemBinding, Tunnel>) (binding, tunnel, position) -> {
@@ -290,7 +296,7 @@ public class TunnelListFragment extends BaseFragment {
     private final class ActionModeListener implements ActionMode.Callback {
         private final Collection<Integer> checkedItems = new HashSet<>();
 
-        private Resources resources;
+        @Nullable private Resources resources;
 
         @Override
         public boolean onActionItemClicked(final ActionMode mode, final MenuItem item) {
@@ -357,7 +363,9 @@ public class TunnelListFragment extends BaseFragment {
                 actionMode.finish();
             }
 
-            binding.tunnelList.getAdapter().notifyItemChanged(position);
+            if (binding != null) {
+                binding.tunnelList.getAdapter().notifyItemChanged(position);
+            }
 
             updateTitle(actionMode);
         }
diff --git a/app/src/main/java/com/wireguard/android/model/ApplicationData.java b/app/src/main/java/com/wireguard/android/model/ApplicationData.java
index 26f81030..73dfb4a9 100644
--- a/app/src/main/java/com/wireguard/android/model/ApplicationData.java
+++ b/app/src/main/java/com/wireguard/android/model/ApplicationData.java
@@ -9,36 +9,32 @@ package com.wireguard.android.model;
 import android.databinding.BaseObservable;
 import android.databinding.Bindable;
 import android.graphics.drawable.Drawable;
-import android.support.annotation.NonNull;
 
 import com.wireguard.android.BR;
 import com.wireguard.util.Keyed;
 
 public class ApplicationData extends BaseObservable implements Keyed<String> {
 
-    @NonNull private final Drawable icon;
-    @NonNull private final String name;
-    @NonNull private final String packageName;
+    private final Drawable icon;
+    private final String name;
+    private final String packageName;
     private boolean excludedFromTunnel;
 
-    public ApplicationData(@NonNull final Drawable icon, @NonNull final String name, @NonNull final String packageName, final boolean excludedFromTunnel) {
+    public ApplicationData(final Drawable icon, final String name, final String packageName, final boolean excludedFromTunnel) {
         this.icon = icon;
         this.name = name;
         this.packageName = packageName;
         this.excludedFromTunnel = excludedFromTunnel;
     }
 
-    @NonNull
     public Drawable getIcon() {
         return icon;
     }
 
-    @NonNull
     public String getName() {
         return name;
     }
 
-    @NonNull
     public String getPackageName() {
         return packageName;
     }
diff --git a/app/src/main/java/com/wireguard/android/model/Tunnel.java b/app/src/main/java/com/wireguard/android/model/Tunnel.java
index 5ea2c0a8..b0d2c1da 100644
--- a/app/src/main/java/com/wireguard/android/model/Tunnel.java
+++ b/app/src/main/java/com/wireguard/android/model/Tunnel.java
@@ -8,13 +8,12 @@ package com.wireguard.android.model;
 
 import android.databinding.BaseObservable;
 import android.databinding.Bindable;
-import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 
 import com.wireguard.android.BR;
 import com.wireguard.android.util.ExceptionLoggers;
-import com.wireguard.util.Keyed;
 import com.wireguard.config.Config;
+import com.wireguard.util.Keyed;
 
 import java.util.regex.Pattern;
 
@@ -30,20 +29,20 @@ public class Tunnel extends BaseObservable implements Keyed<String> {
     private static final Pattern NAME_PATTERN = Pattern.compile("[a-zA-Z0-9_=+.-]{1,15}");
 
     private final TunnelManager manager;
-    private Config config;
+    @Nullable private Config config;
     private String name;
     private State state;
-    private Statistics statistics;
+    @Nullable private Statistics statistics;
 
-    Tunnel(@NonNull final TunnelManager manager, @NonNull final String name,
-           @Nullable final Config config, @NonNull final State state) {
+    Tunnel(final TunnelManager manager, final String name,
+           @Nullable final Config config, final State state) {
         this.manager = manager;
         this.name = name;
         this.config = config;
         this.state = state;
     }
 
-    public static boolean isNameInvalid(@NonNull final CharSequence name) {
+    public static boolean isNameInvalid(final CharSequence name) {
         return !NAME_PATTERN.matcher(name).matches();
     }
 
@@ -51,7 +50,7 @@ public class Tunnel extends BaseObservable implements Keyed<String> {
         return manager.delete(this);
     }
 
-    @Bindable
+    @Bindable @Nullable
     public Config getConfig() {
         if (config == null)
             manager.getTunnelConfig(this).whenComplete(ExceptionLoggers.E);
@@ -83,7 +82,7 @@ public class Tunnel extends BaseObservable implements Keyed<String> {
         return TunnelManager.getTunnelState(this);
     }
 
-    @Bindable
+    @Bindable @Nullable
     public Statistics getStatistics() {
         // FIXME: Check age of statistics.
         if (statistics == null)
@@ -118,25 +117,26 @@ public class Tunnel extends BaseObservable implements Keyed<String> {
         return state;
     }
 
-    Statistics onStatisticsChanged(final Statistics statistics) {
+    @Nullable
+    Statistics onStatisticsChanged(@Nullable final Statistics statistics) {
         this.statistics = statistics;
         notifyPropertyChanged(BR.statistics);
         return statistics;
     }
 
-    public CompletionStage<Config> setConfig(@NonNull final Config config) {
+    public CompletionStage<Config> setConfig(final Config config) {
         if (!config.equals(this.config))
             return manager.setTunnelConfig(this, config);
         return CompletableFuture.completedFuture(this.config);
     }
 
-    public CompletionStage<String> setName(@NonNull final String name) {
+    public CompletionStage<String> setName(final String name) {
         if (!name.equals(this.name))
             return manager.setTunnelName(this, name);
         return CompletableFuture.completedFuture(this.name);
     }
 
-    public CompletionStage<State> setState(@NonNull final State state) {
+    public CompletionStage<State> setState(final State state) {
         if (state != this.state)
             return manager.setTunnelState(this, state);
         return CompletableFuture.completedFuture(this.state);
@@ -152,6 +152,5 @@ public class Tunnel extends BaseObservable implements Keyed<String> {
         }
     }
 
-    public static class Statistics extends BaseObservable {
-    }
+    public static class Statistics extends BaseObservable { }
 }
diff --git a/app/src/main/java/com/wireguard/android/model/TunnelManager.java b/app/src/main/java/com/wireguard/android/model/TunnelManager.java
index a9998d5a..f7b18c07 100644
--- a/app/src/main/java/com/wireguard/android/model/TunnelManager.java
+++ b/app/src/main/java/com/wireguard/android/model/TunnelManager.java
@@ -11,7 +11,7 @@ import android.content.Context;
 import android.content.Intent;
 import android.databinding.BaseObservable;
 import android.databinding.Bindable;
-import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.wireguard.android.Application;
 import com.wireguard.android.BR;
@@ -47,9 +47,8 @@ public final class TunnelManager extends BaseObservable {
     private static final String KEY_RUNNING_TUNNELS = "enabled_configs";
 
     private final ConfigStore configStore;
-    private final ObservableSortedKeyedList<String, Tunnel> tunnels =
-            new ObservableSortedKeyedArrayList<>(COMPARATOR);
-    private Tunnel lastUsedTunnel;
+    private final ObservableSortedKeyedList<String, Tunnel> tunnels = new ObservableSortedKeyedArrayList<>(COMPARATOR);
+    @Nullable private Tunnel lastUsedTunnel;
     private boolean haveLoaded;
     private final ArrayList<CompletableFuture<Void>> delayedLoadRestoreTunnels = new ArrayList<>();
 
@@ -57,13 +56,13 @@ public final class TunnelManager extends BaseObservable {
         this.configStore = configStore;
     }
 
-    private Tunnel addToList(final String name, final Config config, final State state) {
+    private Tunnel addToList(final String name, @Nullable final Config config, final State state) {
         final Tunnel tunnel = new Tunnel(this, name, config, state);
         tunnels.add(tunnel);
         return tunnel;
     }
 
-    public CompletionStage<Tunnel> create(@NonNull final String name, final Config config) {
+    public CompletionStage<Tunnel> create(final String name, @Nullable final Config config) {
         if (Tunnel.isNameInvalid(name))
             return CompletableFuture.failedFuture(new IllegalArgumentException("Invalid name"));
         if (tunnels.containsKey(name)) {
@@ -102,7 +101,7 @@ public final class TunnelManager extends BaseObservable {
         });
     }
 
-    @Bindable
+    @Bindable @Nullable
     public Tunnel getLastUsedTunnel() {
         return lastUsedTunnel;
     }
@@ -191,7 +190,7 @@ public final class TunnelManager extends BaseObservable {
         Application.getSharedPreferences().edit().putStringSet(KEY_RUNNING_TUNNELS, runningTunnels).apply();
     }
 
-    private void setLastUsedTunnel(final Tunnel tunnel) {
+    private void setLastUsedTunnel(@Nullable final Tunnel tunnel) {
         if (tunnel == lastUsedTunnel)
             return;
         lastUsedTunnel = tunnel;
@@ -256,7 +255,7 @@ public final class TunnelManager extends BaseObservable {
 
     public static final class IntentReceiver extends BroadcastReceiver {
         @Override
-        public void onReceive(final Context context, final Intent intent) {
+        public void onReceive(final Context context, @Nullable final Intent intent) {
             final TunnelManager manager = Application.getTunnelManager();
             if (intent == null)
                 return;
diff --git a/app/src/main/java/com/wireguard/android/preference/LogExporterPreference.java b/app/src/main/java/com/wireguard/android/preference/LogExporterPreference.java
index f9ac9a41..a96cb9c8 100644
--- a/app/src/main/java/com/wireguard/android/preference/LogExporterPreference.java
+++ b/app/src/main/java/com/wireguard/android/preference/LogExporterPreference.java
@@ -10,6 +10,7 @@ import android.Manifest;
 import android.content.Context;
 import android.content.pm.PackageManager;
 import android.os.Environment;
+import android.support.annotation.Nullable;
 import android.support.design.widget.Snackbar;
 import android.support.v7.preference.Preference;
 import android.util.AttributeSet;
@@ -33,7 +34,7 @@ import java.io.InputStreamReader;
 public class LogExporterPreference extends Preference {
     private static final String TAG = "WireGuard/" + LogExporterPreference.class.getSimpleName();
 
-    private String exportedFilePath;
+    @Nullable private String exportedFilePath;
 
     public LogExporterPreference(final Context context, final AttributeSet attrs) {
         super(context, attrs);
@@ -73,7 +74,7 @@ public class LogExporterPreference extends Preference {
         }).whenComplete(this::exportLogComplete);
     }
 
-    private void exportLogComplete(final String filePath, final Throwable throwable) {
+    private void exportLogComplete(final String filePath, @Nullable final Throwable throwable) {
         if (throwable != null) {
             final String error = ExceptionLoggers.unwrapMessage(throwable);
             final String message = getContext().getString(R.string.log_export_error, error);
diff --git a/app/src/main/java/com/wireguard/android/preference/ToolsInstallerPreference.java b/app/src/main/java/com/wireguard/android/preference/ToolsInstallerPreference.java
index 44599edc..4006d0e8 100644
--- a/app/src/main/java/com/wireguard/android/preference/ToolsInstallerPreference.java
+++ b/app/src/main/java/com/wireguard/android/preference/ToolsInstallerPreference.java
@@ -7,7 +7,7 @@
 package com.wireguard.android.preference;
 
 import android.content.Context;
-import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.v7.preference.Preference;
 import android.util.AttributeSet;
 
@@ -43,7 +43,7 @@ public class ToolsInstallerPreference extends Preference {
         Application.getAsyncWorker().supplyAsync(Application.getToolsInstaller()::areInstalled).whenComplete(this::onCheckResult);
     }
 
-    private void onCheckResult(final int state, final Throwable throwable) {
+    private void onCheckResult(final int state, @Nullable final Throwable throwable) {
         if (throwable != null || state == ToolsInstaller.ERROR)
             setState(State.INITIAL);
         else if ((state & ToolsInstaller.YES) == ToolsInstaller.YES)
@@ -62,7 +62,7 @@ public class ToolsInstallerPreference extends Preference {
         Application.getAsyncWorker().supplyAsync(Application.getToolsInstaller()::install).whenComplete(this::onInstallResult);
     }
 
-    private void onInstallResult(final Integer result, final Throwable throwable) {
+    private void onInstallResult(final Integer result, @Nullable final Throwable throwable) {
         if (throwable != null)
             setState(State.FAILURE);
         else if ((result & (ToolsInstaller.YES | ToolsInstaller.MAGISK)) == (ToolsInstaller.YES | ToolsInstaller.MAGISK))
@@ -73,7 +73,7 @@ public class ToolsInstallerPreference extends Preference {
             setState(State.FAILURE);
     }
 
-    private void setState(@NonNull final State state) {
+    private void setState(final State state) {
         if (this.state == state)
             return;
         this.state = state;
diff --git a/app/src/main/java/com/wireguard/android/preference/VersionPreference.java b/app/src/main/java/com/wireguard/android/preference/VersionPreference.java
index de34047d..525396bc 100644
--- a/app/src/main/java/com/wireguard/android/preference/VersionPreference.java
+++ b/app/src/main/java/com/wireguard/android/preference/VersionPreference.java
@@ -9,6 +9,7 @@ import android.content.ActivityNotFoundException;
 import android.content.Context;
 import android.content.Intent;
 import android.net.Uri;
+import android.support.annotation.Nullable;
 import android.support.v7.preference.Preference;
 import android.util.AttributeSet;
 
@@ -17,7 +18,7 @@ import com.wireguard.android.BuildConfig;
 import com.wireguard.android.R;
 
 public class VersionPreference extends Preference {
-    private String versionSummary;
+    @Nullable private String versionSummary;
 
     public VersionPreference(final Context context, final AttributeSet attrs) {
         super(context, attrs);
@@ -33,7 +34,7 @@ public class VersionPreference extends Preference {
         });
     }
 
-    @Override
+    @Override @Nullable
     public CharSequence getSummary() {
         return versionSummary;
     }
diff --git a/app/src/main/java/com/wireguard/android/preference/ZipExporterPreference.java b/app/src/main/java/com/wireguard/android/preference/ZipExporterPreference.java
index 16094007..a1477214 100644
--- a/app/src/main/java/com/wireguard/android/preference/ZipExporterPreference.java
+++ b/app/src/main/java/com/wireguard/android/preference/ZipExporterPreference.java
@@ -10,6 +10,7 @@ import android.Manifest;
 import android.content.Context;
 import android.content.pm.PackageManager;
 import android.os.Environment;
+import android.support.annotation.Nullable;
 import android.support.design.widget.Snackbar;
 import android.support.v7.preference.Preference;
 import android.util.AttributeSet;
@@ -40,7 +41,7 @@ import java9.util.concurrent.CompletableFuture;
 public class ZipExporterPreference extends Preference {
     private static final String TAG = "WireGuard/" + ZipExporterPreference.class.getSimpleName();
 
-    private String exportedFilePath;
+    @Nullable private String exportedFilePath;
 
     public ZipExporterPreference(final Context context, final AttributeSet attrs) {
         super(context, attrs);
@@ -79,7 +80,7 @@ public class ZipExporterPreference extends Preference {
                 }).whenComplete(this::exportZipComplete));
     }
 
-    private void exportZipComplete(final String filePath, final Throwable throwable) {
+    private void exportZipComplete(@Nullable final String filePath, @Nullable final Throwable throwable) {
         if (throwable != null) {
             final String error = ExceptionLoggers.unwrapMessage(throwable);
             final String message = getContext().getString(R.string.zip_export_error, error);
diff --git a/app/src/main/java/com/wireguard/android/util/ExceptionLoggers.java b/app/src/main/java/com/wireguard/android/util/ExceptionLoggers.java
index b8c0c4fa..70d97fb1 100644
--- a/app/src/main/java/com/wireguard/android/util/ExceptionLoggers.java
+++ b/app/src/main/java/com/wireguard/android/util/ExceptionLoggers.java
@@ -6,8 +6,9 @@
 
 package com.wireguard.android.util;
 
-import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.util.Log;
+
 import java9.util.concurrent.CompletionException;
 import java9.util.function.BiConsumer;
 
@@ -34,7 +35,6 @@ public enum ExceptionLoggers implements BiConsumer<Object, Throwable> {
         return throwable;
     }
 
-    @NonNull
     public static String unwrapMessage(Throwable throwable) {
         throwable = unwrap(throwable);
         final String message = throwable.getMessage();
@@ -44,7 +44,7 @@ public enum ExceptionLoggers implements BiConsumer<Object, Throwable> {
     }
 
     @Override
-    public void accept(final Object result, final Throwable throwable) {
+    public void accept(final Object result, @Nullable final Throwable throwable) {
         if (throwable != null)
             Log.println(Log.ERROR, TAG, Log.getStackTraceString(throwable));
         else if (priority <= Log.DEBUG)
diff --git a/app/src/main/java/com/wireguard/android/util/ObservableKeyedArrayList.java b/app/src/main/java/com/wireguard/android/util/ObservableKeyedArrayList.java
index 1e064e42..0be3c005 100644
--- a/app/src/main/java/com/wireguard/android/util/ObservableKeyedArrayList.java
+++ b/app/src/main/java/com/wireguard/android/util/ObservableKeyedArrayList.java
@@ -7,7 +7,7 @@
 package com.wireguard.android.util;
 
 import android.databinding.ObservableArrayList;
-import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.wireguard.util.Keyed;
 
@@ -25,28 +25,28 @@ import java.util.Objects;
 public class ObservableKeyedArrayList<K, E extends Keyed<? extends K>>
         extends ObservableArrayList<E> implements ObservableKeyedList<K, E> {
     @Override
-    public boolean add(final E e) {
+    public boolean add(@Nullable final E e) {
         if (e == null)
             throw new NullPointerException("Trying to add a null element");
         return super.add(e);
     }
 
     @Override
-    public void add(final int index, final E e) {
+    public void add(final int index, @Nullable final E e) {
         if (e == null)
             throw new NullPointerException("Trying to add a null element");
         super.add(index, e);
     }
 
     @Override
-    public boolean addAll(@NonNull final Collection<? extends E> c) {
+    public boolean addAll(final Collection<? extends E> c) {
         if (c.contains(null))
             throw new NullPointerException("Trying to add a collection with null element(s)");
         return super.addAll(c);
     }
 
     @Override
-    public boolean addAll(final int index, @NonNull final Collection<? extends E> c) {
+    public boolean addAll(final int index, final Collection<? extends E> c) {
         if (c.contains(null))
             throw new NullPointerException("Trying to add a collection with null element(s)");
         return super.addAll(index, c);
@@ -65,13 +65,13 @@ public class ObservableKeyedArrayList<K, E extends Keyed<? extends K>>
         return indexOfKey(key) >= 0;
     }
 
-    @Override
+    @Override @Nullable
     public E get(final K key) {
         final int index = indexOfKey(key);
         return index >= 0 ? get(index) : null;
     }
 
-    @Override
+    @Override @Nullable
     public E getLast(final K key) {
         final int index = lastIndexOfKey(key);
         return index >= 0 ? get(index) : null;
@@ -100,7 +100,7 @@ public class ObservableKeyedArrayList<K, E extends Keyed<? extends K>>
     }
 
     @Override
-    public E set(final int index, final E e) {
+    public E set(final int index, @Nullable final E e) {
         if (e == null)
             throw new NullPointerException("Trying to set a null key");
         return super.set(index, e);
diff --git a/app/src/main/java/com/wireguard/android/util/ObservableSortedKeyedArrayList.java b/app/src/main/java/com/wireguard/android/util/ObservableSortedKeyedArrayList.java
index 4ff3a771..239520c4 100644
--- a/app/src/main/java/com/wireguard/android/util/ObservableSortedKeyedArrayList.java
+++ b/app/src/main/java/com/wireguard/android/util/ObservableSortedKeyedArrayList.java
@@ -6,7 +6,7 @@
 
 package com.wireguard.android.util;
 
-import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 
 import com.wireguard.util.Keyed;
 import com.wireguard.util.SortedKeyedList;
@@ -29,6 +29,7 @@ import java.util.Spliterator;
 
 public class ObservableSortedKeyedArrayList<K, E extends Keyed<? extends K>>
         extends ObservableKeyedArrayList<K, E> implements ObservableSortedKeyedList<K, E> {
+    @Nullable
     private final Comparator<? super K> comparator;
     private final transient KeyList<K, E> keyList = new KeyList<>(this);
 
@@ -75,7 +76,7 @@ public class ObservableSortedKeyedArrayList<K, E extends Keyed<? extends K>>
     }
 
     @Override
-    public boolean addAll(@NonNull final Collection<? extends E> c) {
+    public boolean addAll(final Collection<? extends E> c) {
         boolean didChange = false;
         for (final E e : c)
             if (add(e))
@@ -84,12 +85,13 @@ public class ObservableSortedKeyedArrayList<K, E extends Keyed<? extends K>>
     }
 
     @Override
-    public boolean addAll(int index, @NonNull final Collection<? extends E> c) {
+    public boolean addAll(int index, final Collection<? extends E> c) {
         for (final E e : c)
             add(index++, e);
         return true;
     }
 
+    @Nullable
     @Override
     public Comparator<? super K> comparator() {
         return comparator;
@@ -128,7 +130,6 @@ public class ObservableSortedKeyedArrayList<K, E extends Keyed<? extends K>>
     }
 
     @Override
-    @NonNull
     public Set<K> keySet() {
         return keyList;
     }
@@ -168,7 +169,6 @@ public class ObservableSortedKeyedArrayList<K, E extends Keyed<? extends K>>
     }
 
     @Override
-    @NonNull
     public Collection<E> values() {
         return this;
     }
diff --git a/app/src/main/java/com/wireguard/android/util/RootShell.java b/app/src/main/java/com/wireguard/android/util/RootShell.java
index 9293dff9..18e04102 100644
--- a/app/src/main/java/com/wireguard/android/util/RootShell.java
+++ b/app/src/main/java/com/wireguard/android/util/RootShell.java
@@ -7,6 +7,7 @@
 package com.wireguard.android.util;
 
 import android.content.Context;
+import android.support.annotation.Nullable;
 import android.util.Log;
 
 import com.wireguard.android.R;
@@ -34,10 +35,10 @@ public class RootShell {
     private final File localTemporaryDir;
     private final Object lock = new Object();
     private final String preamble;
-    private Process process;
-    private BufferedReader stderr;
-    private OutputStreamWriter stdin;
-    private BufferedReader stdout;
+    @Nullable private Process process;
+    @Nullable private BufferedReader stderr;
+    @Nullable private OutputStreamWriter stdin;
+    @Nullable private BufferedReader stdout;
 
     public RootShell(final Context context) {
         deviceNotRootedMessage = context.getString(R.string.error_root);
@@ -80,7 +81,7 @@ public class RootShell {
      * @param command Command to run as root.
      * @return The exit value of the command.
      */
-    public int run(final Collection<String> output, final String command)
+    public int run(@Nullable final Collection<String> output, final String command)
             throws IOException, NoRootException {
         synchronized (lock) {
             /* Start inside synchronized block to prevent a concurrent call to stop(). */
diff --git a/app/src/main/java/com/wireguard/android/util/SharedLibraryLoader.java b/app/src/main/java/com/wireguard/android/util/SharedLibraryLoader.java
index e0bb579d..997dd45c 100644
--- a/app/src/main/java/com/wireguard/android/util/SharedLibraryLoader.java
+++ b/app/src/main/java/com/wireguard/android/util/SharedLibraryLoader.java
@@ -19,8 +19,7 @@ import java.util.zip.ZipFile;
 public final class SharedLibraryLoader {
     private static final String TAG = "WireGuard/" + SharedLibraryLoader.class.getSimpleName();
 
-    private SharedLibraryLoader() {
-    }
+    private SharedLibraryLoader() { }
 
     public static void loadSharedLibrary(final Context context, final String libName) {
         Throwable noAbiException;
diff --git a/app/src/main/java/com/wireguard/android/util/ToolsInstaller.java b/app/src/main/java/com/wireguard/android/util/ToolsInstaller.java
index 9cdb6a59..16c906eb 100644
--- a/app/src/main/java/com/wireguard/android/util/ToolsInstaller.java
+++ b/app/src/main/java/com/wireguard/android/util/ToolsInstaller.java
@@ -7,6 +7,7 @@
 package com.wireguard.android.util;
 
 import android.content.Context;
+import android.support.annotation.Nullable;
 import android.system.OsConstants;
 import android.util.Log;
 
@@ -39,20 +40,21 @@ public final class ToolsInstaller {
             new File("/system/xbin"),
             new File("/system/bin"),
     };
-    private static final File INSTALL_DIR = getInstallDir();
+    @Nullable private static final File INSTALL_DIR = getInstallDir();
     private static final String TAG = "WireGuard/" + ToolsInstaller.class.getSimpleName();
 
     private final File localBinaryDir;
     private final Object lock = new Object();
     private final File nativeLibraryDir;
-    private Boolean areToolsAvailable;
-    private Boolean installAsMagiskModule;
+    @Nullable private Boolean areToolsAvailable;
+    @Nullable private Boolean installAsMagiskModule;
 
     public ToolsInstaller(final Context context) {
         localBinaryDir = new File(context.getCacheDir(), "bin");
         nativeLibraryDir = new File(context.getApplicationInfo().nativeLibraryDir);
     }
 
+    @Nullable
     private static File getInstallDir() {
         final String path = System.getenv("PATH");
         if (path == null)
diff --git a/app/src/main/java/com/wireguard/android/widget/KeyInputFilter.java b/app/src/main/java/com/wireguard/android/widget/KeyInputFilter.java
index fff3bc22..a7c11717 100644
--- a/app/src/main/java/com/wireguard/android/widget/KeyInputFilter.java
+++ b/app/src/main/java/com/wireguard/android/widget/KeyInputFilter.java
@@ -6,6 +6,7 @@
 
 package com.wireguard.android.widget;
 
+import android.support.annotation.Nullable;
 import android.text.InputFilter;
 import android.text.SpannableStringBuilder;
 import android.text.Spanned;
@@ -25,7 +26,7 @@ public class KeyInputFilter implements InputFilter {
         return new KeyInputFilter();
     }
 
-    @Override
+    @Override @Nullable
     public CharSequence filter(final CharSequence source,
                                final int sStart, final int sEnd,
                                final Spanned dest,
diff --git a/app/src/main/java/com/wireguard/android/widget/NameInputFilter.java b/app/src/main/java/com/wireguard/android/widget/NameInputFilter.java
index b31c9176..514b9f88 100644
--- a/app/src/main/java/com/wireguard/android/widget/NameInputFilter.java
+++ b/app/src/main/java/com/wireguard/android/widget/NameInputFilter.java
@@ -6,6 +6,7 @@
 
 package com.wireguard.android.widget;
 
+import android.support.annotation.Nullable;
 import android.text.InputFilter;
 import android.text.SpannableStringBuilder;
 import android.text.Spanned;
@@ -25,7 +26,7 @@ public class NameInputFilter implements InputFilter {
         return new NameInputFilter();
     }
 
-    @Override
+    @Override @Nullable
     public CharSequence filter(final CharSequence source,
                                final int sStart, final int sEnd,
                                final Spanned dest,
diff --git a/app/src/main/java/com/wireguard/android/widget/SlashDrawable.java b/app/src/main/java/com/wireguard/android/widget/SlashDrawable.java
index 64fe7f73..53530e0a 100644
--- a/app/src/main/java/com/wireguard/android/widget/SlashDrawable.java
+++ b/app/src/main/java/com/wireguard/android/widget/SlashDrawable.java
@@ -25,11 +25,9 @@ import android.graphics.drawable.Drawable;
 import android.os.Build;
 import android.support.annotation.ColorInt;
 import android.support.annotation.IntRange;
-import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 import android.util.FloatProperty;
 
-
 @TargetApi(Build.VERSION_CODES.N)
 public class SlashDrawable extends Drawable {
 
@@ -53,26 +51,24 @@ public class SlashDrawable extends Drawable {
     // Draw the slash washington-monument style; rotate to no-u-turn style
     private static final float DEFAULT_ROTATION = -45f;
 
-    private Drawable mDrawable;
+    private final Drawable mDrawable;
     private final RectF mSlashRect = new RectF(0, 0, 0, 0);
     private float mRotation;
     private boolean mSlashed;
-    private Mode mTintMode;
-    private ColorStateList mTintList;
     private boolean mAnimationEnabled = true;
 
     public SlashDrawable(final Drawable d) {
-        setDrawable(d);
+        mDrawable = d;
     }
 
     @Override
     public int getIntrinsicHeight() {
-        return mDrawable != null ? mDrawable.getIntrinsicHeight(): 0;
+        return mDrawable.getIntrinsicHeight();
     }
 
     @Override
     public int getIntrinsicWidth() {
-        return mDrawable != null ? mDrawable.getIntrinsicWidth(): 0;
+        return mDrawable.getIntrinsicWidth();
     }
 
     @Override
@@ -81,17 +77,6 @@ public class SlashDrawable extends Drawable {
         mDrawable.setBounds(bounds);
     }
 
-    public void setDrawable(final Drawable d) {
-        mDrawable = d;
-        mDrawable.setCallback(getCallback());
-        mDrawable.setBounds(getBounds());
-        if (mTintMode != null)
-            mDrawable.setTintMode(mTintMode);
-        if (mTintList != null)
-            mDrawable.setTintList(mTintList);
-        invalidateSelf();
-    }
-
     public void setRotation(final float rotation) {
         if (mRotation == rotation)
             return;
@@ -139,7 +124,7 @@ public class SlashDrawable extends Drawable {
 
     @SuppressWarnings("deprecation")
     @Override
-    public void draw(@NonNull final Canvas canvas) {
+    public void draw(final Canvas canvas) {
         canvas.save();
         final Matrix m = new Matrix();
         final int width = getBounds().width();
@@ -201,7 +186,6 @@ public class SlashDrawable extends Drawable {
 
     @Override
     public void setTintList(@Nullable final ColorStateList tint) {
-        mTintList = tint;
         super.setTintList(tint);
         setDrawableTintList(tint);
         mPaint.setColor(tint == null ? 0 : tint.getDefaultColor());
@@ -213,8 +197,7 @@ public class SlashDrawable extends Drawable {
     }
 
     @Override
-    public void setTintMode(@NonNull final Mode tintMode) {
-        mTintMode = tintMode;
+    public void setTintMode(final Mode tintMode) {
         super.setTintMode(tintMode);
         mDrawable.setTintMode(tintMode);
     }
diff --git a/app/src/main/java/com/wireguard/android/widget/ToggleSwitch.java b/app/src/main/java/com/wireguard/android/widget/ToggleSwitch.java
index b71ad447..b2928293 100644
--- a/app/src/main/java/com/wireguard/android/widget/ToggleSwitch.java
+++ b/app/src/main/java/com/wireguard/android/widget/ToggleSwitch.java
@@ -7,22 +7,23 @@ package com.wireguard.android.widget;
 
 import android.content.Context;
 import android.os.Parcelable;
+import android.support.annotation.Nullable;
 import android.util.AttributeSet;
 import android.widget.Switch;
 
 public class ToggleSwitch extends Switch {
     private boolean isRestoringState;
-    private OnBeforeCheckedChangeListener listener;
-
-    @SuppressWarnings({"SameParameterValue", "WeakerAccess"})
-    public ToggleSwitch(final Context context, final AttributeSet attrs) {
-        super(context, attrs);
-    }
+    @Nullable private OnBeforeCheckedChangeListener listener;
 
     public ToggleSwitch(final Context context) {
         this(context, null);
     }
 
+    @SuppressWarnings({"SameParameterValue", "WeakerAccess"})
+    public ToggleSwitch(final Context context, @Nullable final AttributeSet attrs) {
+        super(context, attrs);
+    }
+
     @Override
     public void onRestoreInstanceState(final Parcelable state) {
         isRestoringState = true;
diff --git a/app/src/main/java/com/wireguard/android/widget/fab/FloatingActionsMenu.java b/app/src/main/java/com/wireguard/android/widget/fab/FloatingActionsMenu.java
index fb87b1e9..7ca6d976 100644
--- a/app/src/main/java/com/wireguard/android/widget/fab/FloatingActionsMenu.java
+++ b/app/src/main/java/com/wireguard/android/widget/fab/FloatingActionsMenu.java
@@ -20,7 +20,7 @@ import android.graphics.drawable.LayerDrawable;
 import android.os.Parcel;
 import android.os.Parcelable;
 import android.support.annotation.Keep;
-import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.support.design.widget.FloatingActionButton;
 import android.support.v4.content.res.ResourcesCompat;
 import android.support.v7.widget.AppCompatTextView;
@@ -57,32 +57,32 @@ public class FloatingActionsMenu extends ViewGroup {
     private boolean mExpanded;
     private final AnimatorSet mExpandAnimation = new AnimatorSet().setDuration(ANIMATION_DURATION);
     private final AnimatorSet mCollapseAnimation = new AnimatorSet().setDuration(ANIMATION_DURATION);
-    private FloatingActionButton mAddButton;
-    private RotatingDrawable mRotatingDrawable;
+    @Nullable private FloatingActionButton mAddButton;
+    @Nullable private RotatingDrawable mRotatingDrawable;
     private int mMaxButtonWidth;
     private int mMaxButtonHeight;
     private int mLabelsStyle;
     private int mLabelsPosition;
     private int mButtonsCount;
-    private TouchDelegateGroup mTouchDelegateGroup;
-    private OnFloatingActionsMenuUpdateListener mListener;
+    @Nullable private TouchDelegateGroup mTouchDelegateGroup;
+    @Nullable private OnFloatingActionsMenuUpdateListener mListener;
     private final Rect touchArea = new Rect(0, 0, 0, 0);
 
     public FloatingActionsMenu(final Context context) {
         this(context, null);
     }
 
-    public FloatingActionsMenu(final Context context, final AttributeSet attrs) {
+    public FloatingActionsMenu(final Context context, @Nullable final AttributeSet attrs) {
         super(context, attrs);
         init(context, attrs);
     }
 
-    public FloatingActionsMenu(final Context context, final AttributeSet attrs, final int defStyle) {
+    public FloatingActionsMenu(final Context context, @Nullable final AttributeSet attrs, final int defStyle) {
         super(context, attrs, defStyle);
         init(context, attrs);
     }
 
-    private void init(final Context context, final AttributeSet attributeSet) {
+    private void init(final Context context, @Nullable final AttributeSet attributeSet) {
         mButtonSpacing = (int) (getResources().getDimension(R.dimen.fab_actions_spacing));
         mLabelsMargin = getResources().getDimensionPixelSize(R.dimen.fab_labels_margin);
         mLabelsVerticalOffset = getResources().getDimensionPixelSize(R.dimen.fab_shadow_offset);
@@ -530,7 +530,7 @@ public class FloatingActionsMenu extends ViewGroup {
         }
 
         @Override
-        public void writeToParcel(@NonNull final Parcel out, final int flags) {
+        public void writeToParcel(final Parcel out, final int flags) {
             super.writeToParcel(out, flags);
             out.writeInt(mExpanded ? 1 : 0);
         }
diff --git a/app/src/main/java/com/wireguard/android/widget/fab/LabeledFloatingActionButton.java b/app/src/main/java/com/wireguard/android/widget/fab/LabeledFloatingActionButton.java
index a203282e..cc6c97cc 100644
--- a/app/src/main/java/com/wireguard/android/widget/fab/LabeledFloatingActionButton.java
+++ b/app/src/main/java/com/wireguard/android/widget/fab/LabeledFloatingActionButton.java
@@ -8,6 +8,7 @@ package com.wireguard.android.widget.fab;
 
 import android.content.Context;
 import android.content.res.TypedArray;
+import android.support.annotation.Nullable;
 import android.support.design.widget.FloatingActionButton;
 import android.util.AttributeSet;
 import android.widget.TextView;
@@ -16,17 +17,17 @@ import com.wireguard.android.R;
 
 public class LabeledFloatingActionButton extends FloatingActionButton {
 
-    private final String title;
+    @Nullable private final String title;
 
     public LabeledFloatingActionButton(final Context context) {
         this(context, null);
     }
 
-    public LabeledFloatingActionButton(final Context context, final AttributeSet attrs) {
+    public LabeledFloatingActionButton(final Context context, @Nullable final AttributeSet attrs) {
         this(context, attrs, 0);
     }
 
-    public LabeledFloatingActionButton(final Context context, final AttributeSet attrs, final int defStyle) {
+    public LabeledFloatingActionButton(final Context context, @Nullable final AttributeSet attrs, final int defStyle) {
         super(context, attrs, defStyle);
 
         final TypedArray attr = context.obtainStyledAttributes(attrs, R.styleable.LabeledFloatingActionButton, 0, 0);
@@ -34,10 +35,12 @@ public class LabeledFloatingActionButton extends FloatingActionButton {
         attr.recycle();
     }
 
+    @Nullable
     TextView getLabelView() {
         return (TextView) getTag(R.id.fab_label);
     }
 
+    @Nullable
     public String getTitle() {
         return title;
     }
diff --git a/app/src/main/java/com/wireguard/android/widget/fab/TouchDelegateGroup.java b/app/src/main/java/com/wireguard/android/widget/fab/TouchDelegateGroup.java
index f6152934..6812f885 100644
--- a/app/src/main/java/com/wireguard/android/widget/fab/TouchDelegateGroup.java
+++ b/app/src/main/java/com/wireguard/android/widget/fab/TouchDelegateGroup.java
@@ -7,7 +7,7 @@
 package com.wireguard.android.widget.fab;
 
 import android.graphics.Rect;
-import android.support.annotation.NonNull;
+import android.support.annotation.Nullable;
 import android.view.MotionEvent;
 import android.view.TouchDelegate;
 import android.view.View;
@@ -18,14 +18,14 @@ import java.util.Collection;
 public class TouchDelegateGroup extends TouchDelegate {
     private static final Rect USELESS_HACKY_RECT = new Rect();
     private final Collection<TouchDelegate> mTouchDelegates = new ArrayList<>();
-    private TouchDelegate mCurrentTouchDelegate;
+    @Nullable private TouchDelegate mCurrentTouchDelegate;
     private boolean mEnabled;
 
     public TouchDelegateGroup(final View uselessHackyView) {
         super(USELESS_HACKY_RECT, uselessHackyView);
     }
 
-    public void addTouchDelegate(@NonNull final TouchDelegate touchDelegate) {
+    public void addTouchDelegate(final TouchDelegate touchDelegate) {
         mTouchDelegates.add(touchDelegate);
     }
 
@@ -42,7 +42,7 @@ public class TouchDelegateGroup extends TouchDelegate {
     }
 
     @Override
-    public boolean onTouchEvent(@NonNull final MotionEvent event) {
+    public boolean onTouchEvent(final MotionEvent event) {
         if (!mEnabled)
             return false;
 
diff --git a/app/src/main/java/com/wireguard/config/Attribute.java b/app/src/main/java/com/wireguard/config/Attribute.java
index bd9fa05d..e8b731b5 100644
--- a/app/src/main/java/com/wireguard/config/Attribute.java
+++ b/app/src/main/java/com/wireguard/config/Attribute.java
@@ -6,6 +6,7 @@
 
 package com.wireguard.config;
 
+import android.support.annotation.Nullable;
 import android.text.TextUtils;
 
 import java.util.HashMap;
@@ -59,13 +60,13 @@ public enum Attribute {
         return KEY_MAP.get(SEPARATOR_PATTERN.split(line)[0].toLowerCase());
     }
 
-    public static String[] stringToList(final String string) {
+    public static String[] stringToList(@Nullable final String string) {
         if (TextUtils.isEmpty(string))
             return EMPTY_LIST;
         return LIST_SEPARATOR_PATTERN.split(string.trim());
     }
 
-    public String composeWith(final Object value) {
+    public String composeWith(@Nullable final Object value) {
         return String.format("%s = %s%n", token, value);
     }
 
@@ -77,11 +78,13 @@ public enum Attribute {
         return String.format("%s = %s%n", token, iterableToString(value));
     }
 
+    @Nullable
     public String parse(final CharSequence line) {
         final Matcher matcher = pattern.matcher(line);
         return matcher.matches() ? matcher.group(1) : null;
     }
 
+    @Nullable
     public String[] parseList(final CharSequence line) {
         final Matcher matcher = pattern.matcher(line);
         return matcher.matches() ? stringToList(matcher.group(1)) : null;
diff --git a/app/src/main/java/com/wireguard/config/Config.java b/app/src/main/java/com/wireguard/config/Config.java
index 62ba252c..0599dec3 100644
--- a/app/src/main/java/com/wireguard/config/Config.java
+++ b/app/src/main/java/com/wireguard/config/Config.java
@@ -12,6 +12,7 @@ import android.databinding.ObservableArrayList;
 import android.databinding.ObservableList;
 import android.os.Parcel;
 import android.os.Parcelable;
+import android.support.annotation.Nullable;
 
 import com.android.databinding.library.baseAdapters.BR;
 
@@ -96,13 +97,19 @@ public class Config {
                 return new Observable[size];
             }
         };
-        private String name;
-        private Interface.Observable observableInterface;
-        private ObservableList<Peer.Observable> observablePeers;
+        @Nullable private String name;
+        private final Interface.Observable observableInterface;
+        private final ObservableList<Peer.Observable> observablePeers;
 
-        public Observable(final Config parent, final String name) {
+        public Observable(@Nullable final Config parent, @Nullable final String name) {
             this.name = name;
-            loadData(parent);
+
+            observableInterface = new Interface.Observable(parent == null ? null : parent.interfaceSection);
+            observablePeers = new ObservableArrayList<>();
+            if (parent != null) {
+                for (final Peer peer : parent.getPeers())
+                    observablePeers.add(new Peer.Observable(peer));
+            }
         }
 
         private Observable(final Parcel in) {
@@ -144,15 +151,6 @@ public class Config {
             return observablePeers;
         }
 
-        protected void loadData(final Config parent) {
-            observableInterface = new Interface.Observable(parent == null ? null : parent.interfaceSection);
-            observablePeers = new ObservableArrayList<>();
-            if (parent != null) {
-                for (final Peer peer : parent.getPeers())
-                    observablePeers.add(new Peer.Observable(peer));
-            }
-        }
-
         public void setName(final String name) {
             this.name = name;
             notifyPropertyChanged(BR.name);
diff --git a/app/src/main/java/com/wireguard/config/InetAddresses.java b/app/src/main/java/com/wireguard/config/InetAddresses.java
index b943f03e..3cc84b01 100644
--- a/app/src/main/java/com/wireguard/config/InetAddresses.java
+++ b/app/src/main/java/com/wireguard/config/InetAddresses.java
@@ -6,7 +6,6 @@
 
 package com.wireguard.config;
 
-import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
 
 import java.lang.reflect.InvocationTargetException;
@@ -29,7 +28,6 @@ public final class InetAddresses {
         // Prevent instantiation.
     }
 
-    @NonNull
     public static InetAddress parse(@Nullable final String address) {
         if (address == null || address.isEmpty())
             throw new IllegalArgumentException("Empty address");
diff --git a/app/src/main/java/com/wireguard/config/InetNetwork.java b/app/src/main/java/com/wireguard/config/InetNetwork.java
index 6f1be914..8f434753 100644
--- a/app/src/main/java/com/wireguard/config/InetNetwork.java
+++ b/app/src/main/java/com/wireguard/config/InetNetwork.java
@@ -6,8 +6,6 @@
 
 package com.wireguard.config;
 
-import android.support.annotation.NonNull;
-
 import java.net.Inet4Address;
 import java.net.InetAddress;
 import java.util.Objects;
@@ -16,7 +14,7 @@ public class InetNetwork {
     private final InetAddress address;
     private final int mask;
 
-    public InetNetwork(@NonNull final String input) {
+    public InetNetwork(final String input) {
         final int slash = input.lastIndexOf('/');
         final int rawMask;
         final String rawAddress;
@@ -40,7 +38,6 @@ public class InetNetwork {
         return Objects.equals(address, other.address) && mask == other.mask;
     }
 
-    @NonNull
     public InetAddress getAddress() {
         return address;
     }
diff --git a/app/src/main/java/com/wireguard/config/Interface.java b/app/src/main/java/com/wireguard/config/Interface.java
index 3f72e812..99336ae4 100644
--- a/app/src/main/java/com/wireguard/config/Interface.java
+++ b/app/src/main/java/com/wireguard/config/Interface.java
@@ -10,6 +10,7 @@ import android.databinding.BaseObservable;
 import android.databinding.Bindable;
 import android.os.Parcel;
 import android.os.Parcelable;
+import android.support.annotation.Nullable;
 
 import com.wireguard.android.BR;
 import com.wireguard.crypto.Keypair;
@@ -27,7 +28,7 @@ public class Interface {
     private final List<InetNetwork> addressList;
     private final List<InetAddress> dnsList;
     private final List<String> excludedApplications;
-    private Keypair keypair;
+    @Nullable private Keypair keypair;
     private int listenPort;
     private int mtu;
 
@@ -37,7 +38,7 @@ public class Interface {
         excludedApplications = new ArrayList<>();
     }
 
-    private void addAddresses(final String[] addresses) {
+    private void addAddresses(@Nullable final String[] addresses) {
         if (addresses != null && addresses.length > 0) {
             for (final String addr : addresses) {
                 if (addr.isEmpty())
@@ -47,7 +48,7 @@ public class Interface {
         }
     }
 
-    private void addDnses(final String[] dnses) {
+    private void addDnses(@Nullable final String[] dnses) {
         if (dnses != null && dnses.length > 0) {
             for (final String dns : dnses) {
                 dnsList.add(InetAddresses.parse(dns));
@@ -55,12 +56,13 @@ public class Interface {
         }
     }
 
-    private void addExcludedApplications(final String[] applications) {
+    private void addExcludedApplications(@Nullable final String[] applications) {
         if (applications != null && applications.length > 0) {
             excludedApplications.addAll(Arrays.asList(applications));
         }
     }
 
+    @Nullable
     private String getAddressString() {
         if (addressList.isEmpty())
             return null;
@@ -71,6 +73,7 @@ public class Interface {
         return addressList.toArray(new InetNetwork[addressList.size()]);
     }
 
+    @Nullable
     private String getDnsString() {
         if (dnsList.isEmpty())
             return null;
@@ -88,6 +91,7 @@ public class Interface {
         return dnsList.toArray(new InetAddress[dnsList.size()]);
     }
 
+    @Nullable
     private String getExcludedApplicationsString() {
         if (excludedApplications.isEmpty())
             return null;
@@ -102,6 +106,7 @@ public class Interface {
         return listenPort;
     }
 
+    @Nullable
     private String getListenPortString() {
         if (listenPort == 0)
             return null;
@@ -112,18 +117,21 @@ public class Interface {
         return mtu;
     }
 
+    @Nullable
     private String getMtuString() {
         if (mtu == 0)
             return null;
         return Integer.toString(mtu);
     }
 
+    @Nullable
     public String getPrivateKey() {
         if (keypair == null)
             return null;
         return keypair.getPrivateKey();
     }
 
+    @Nullable
     public String getPublicKey() {
         if (keypair == null)
             return null;
@@ -156,17 +164,17 @@ public class Interface {
         }
     }
 
-    private void setAddressString(final String addressString) {
+    private void setAddressString(@Nullable final String addressString) {
         addressList.clear();
         addAddresses(Attribute.stringToList(addressString));
     }
 
-    private void setDnsString(final String dnsString) {
+    private void setDnsString(@Nullable final String dnsString) {
         dnsList.clear();
         addDnses(Attribute.stringToList(dnsString));
     }
 
-    private void setExcludedApplicationsString(final String applicationsString) {
+    private void setExcludedApplicationsString(@Nullable final String applicationsString) {
         excludedApplications.clear();
         addExcludedApplications(Attribute.stringToList(applicationsString));
     }
@@ -175,7 +183,7 @@ public class Interface {
         this.listenPort = listenPort;
     }
 
-    private void setListenPortString(final String port) {
+    private void setListenPortString(@Nullable final String port) {
         if (port != null && !port.isEmpty())
             setListenPort(Integer.parseInt(port, 10));
         else
@@ -186,14 +194,14 @@ public class Interface {
         this.mtu = mtu;
     }
 
-    private void setMtuString(final String mtu) {
+    private void setMtuString(@Nullable final String mtu) {
         if (mtu != null && !mtu.isEmpty())
             setMtu(Integer.parseInt(mtu, 10));
         else
             setMtu(0);
     }
 
-    private void setPrivateKey(String privateKey) {
+    private void setPrivateKey(@Nullable String privateKey) {
         if (privateKey != null && privateKey.isEmpty())
             privateKey = null;
         keypair = privateKey == null ? null : new Keypair(privateKey);
@@ -229,15 +237,15 @@ public class Interface {
                 return new Observable[size];
             }
         };
-        private String addresses;
-        private String dnses;
-        private String excludedApplications;
-        private String listenPort;
-        private String mtu;
-        private String privateKey;
-        private String publicKey;
+        @Nullable private String addresses;
+        @Nullable private String dnses;
+        @Nullable private String excludedApplications;
+        @Nullable private String listenPort;
+        @Nullable private String mtu;
+        @Nullable private String privateKey;
+        @Nullable private String publicKey;
 
-        public Observable(final Interface parent) {
+        public Observable(@Nullable final Interface parent) {
             if (parent != null)
                 loadData(parent);
         }
@@ -276,16 +284,19 @@ public class Interface {
             notifyPropertyChanged(BR.publicKey);
         }
 
+        @Nullable
         @Bindable
         public String getAddresses() {
             return addresses;
         }
 
+        @Nullable
         @Bindable
         public String getDnses() {
             return dnses;
         }
 
+        @Nullable
         @Bindable
         public String getExcludedApplications() {
             return excludedApplications;
@@ -296,21 +307,25 @@ public class Interface {
             return Attribute.stringToList(excludedApplications).length;
         }
 
+        @Nullable
         @Bindable
         public String getListenPort() {
             return listenPort;
         }
 
+        @Nullable
         @Bindable
         public String getMtu() {
             return mtu;
         }
 
+        @Nullable
         @Bindable
         public String getPrivateKey() {
             return privateKey;
         }
 
+        @Nullable
         @Bindable
         public String getPublicKey() {
             return publicKey;
diff --git a/app/src/main/java/com/wireguard/config/Peer.java b/app/src/main/java/com/wireguard/config/Peer.java
index 371072de..60fe5c82 100644
--- a/app/src/main/java/com/wireguard/config/Peer.java
+++ b/app/src/main/java/com/wireguard/config/Peer.java
@@ -10,6 +10,7 @@ import android.databinding.BaseObservable;
 import android.databinding.Bindable;
 import android.os.Parcel;
 import android.os.Parcelable;
+import android.support.annotation.Nullable;
 
 import com.android.databinding.library.baseAdapters.BR;
 import com.wireguard.crypto.KeyEncoding;
@@ -34,16 +35,16 @@ import java9.lang.Iterables;
 
 public class Peer {
     private final List<InetNetwork> allowedIPsList;
-    private InetSocketAddress endpoint;
+    @Nullable private InetSocketAddress endpoint;
     private int persistentKeepalive;
-    private String preSharedKey;
-    private String publicKey;
+    @Nullable private String preSharedKey;
+    @Nullable private String publicKey;
 
     public Peer() {
         allowedIPsList = new ArrayList<>();
     }
 
-    private void addAllowedIPs(final String[] allowedIPs) {
+    private void addAllowedIPs(@Nullable final String[] allowedIPs) {
         if (allowedIPs != null && allowedIPs.length > 0) {
             for (final String allowedIP : allowedIPs) {
                 allowedIPsList.add(new InetNetwork(allowedIP));
@@ -55,16 +56,19 @@ public class Peer {
         return allowedIPsList.toArray(new InetNetwork[allowedIPsList.size()]);
     }
 
+    @Nullable
     private String getAllowedIPsString() {
         if (allowedIPsList.isEmpty())
             return null;
         return Attribute.iterableToString(allowedIPsList);
     }
 
+    @Nullable
     public InetSocketAddress getEndpoint() {
         return endpoint;
     }
 
+    @Nullable
     private String getEndpointString() {
         if (endpoint == null)
             return null;
@@ -75,16 +79,19 @@ public class Peer {
         return persistentKeepalive;
     }
 
+    @Nullable
     private String getPersistentKeepaliveString() {
         if (persistentKeepalive == 0)
             return null;
         return Integer.valueOf(persistentKeepalive).toString();
     }
 
+    @Nullable
     public String getPreSharedKey() {
         return preSharedKey;
     }
 
+    @Nullable
     public String getPublicKey() {
         return publicKey;
     }
@@ -130,16 +137,16 @@ public class Peer {
         }
     }
 
-    private void setAllowedIPsString(final String allowedIPsString) {
+    private void setAllowedIPsString(@Nullable final String allowedIPsString) {
         allowedIPsList.clear();
         addAllowedIPs(Attribute.stringToList(allowedIPsString));
     }
 
-    private void setEndpoint(final InetSocketAddress endpoint) {
+    private void setEndpoint(@Nullable final InetSocketAddress endpoint) {
         this.endpoint = endpoint;
     }
 
-    private void setEndpointString(final String endpoint) {
+    private void setEndpointString(@Nullable final String endpoint) {
         if (endpoint != null && !endpoint.isEmpty()) {
             final InetSocketAddress constructedEndpoint;
             if (endpoint.indexOf('/') != -1 || endpoint.indexOf('?') != -1 || endpoint.indexOf('#') != -1)
@@ -160,14 +167,14 @@ public class Peer {
         this.persistentKeepalive = persistentKeepalive;
     }
 
-    private void setPersistentKeepaliveString(final String persistentKeepalive) {
+    private void setPersistentKeepaliveString(@Nullable final String persistentKeepalive) {
         if (persistentKeepalive != null && !persistentKeepalive.isEmpty())
             setPersistentKeepalive(Integer.parseInt(persistentKeepalive, 10));
         else
             setPersistentKeepalive(0);
     }
 
-    private void setPreSharedKey(String preSharedKey) {
+    private void setPreSharedKey(@Nullable String preSharedKey) {
         if (preSharedKey != null && preSharedKey.isEmpty())
             preSharedKey = null;
         if (preSharedKey != null)
@@ -175,7 +182,7 @@ public class Peer {
         this.preSharedKey = preSharedKey;
     }
 
-    private void setPublicKey(String publicKey) {
+    private void setPublicKey(@Nullable String publicKey) {
         if (publicKey != null && publicKey.isEmpty())
             publicKey = null;
         if (publicKey != null)
@@ -211,12 +218,12 @@ public class Peer {
                 return new Observable[size];
             }
         };
-        private String allowedIPs;
-        private String endpoint;
-        private String persistentKeepalive;
-        private String preSharedKey;
-        private String publicKey;
-        private List<String> interfaceDNSRoutes;
+        @Nullable private String allowedIPs;
+        @Nullable private String endpoint;
+        @Nullable private String persistentKeepalive;
+        @Nullable private String preSharedKey;
+        @Nullable private String publicKey;
+        private final List<String> interfaceDNSRoutes = new ArrayList<>();
         private int numSiblings;
 
         public Observable(final Peer parent) {
@@ -230,7 +237,6 @@ public class Peer {
             preSharedKey = in.readString();
             publicKey = in.readString();
             numSiblings = in.readInt();
-            interfaceDNSRoutes = new ArrayList<>();
             in.readStringList(interfaceDNSRoutes);
         }
 
@@ -284,27 +290,27 @@ public class Peer {
             return numSiblings == 0 && Arrays.asList(Attribute.stringToList(allowedIPs)).containsAll(DEFAULT_ROUTE_MOD_RFC1918_V4);
         }
 
-        @Bindable
+        @Bindable @Nullable
         public String getAllowedIPs() {
             return allowedIPs;
         }
 
-        @Bindable
+        @Bindable @Nullable
         public String getEndpoint() {
             return endpoint;
         }
 
-        @Bindable
+        @Bindable @Nullable
         public String getPersistentKeepalive() {
             return persistentKeepalive;
         }
 
-        @Bindable
+        @Bindable @Nullable
         public String getPreSharedKey() {
             return preSharedKey;
         }
 
-        @Bindable
+        @Bindable @Nullable
         public String getPublicKey() {
             return publicKey;
         }
@@ -315,7 +321,6 @@ public class Peer {
             persistentKeepalive = parent.getPersistentKeepaliveString();
             preSharedKey = parent.getPreSharedKey();
             publicKey = parent.getPublicKey();
-            interfaceDNSRoutes = new ArrayList<>();
         }
 
         public void setAllowedIPs(final String allowedIPs) {
diff --git a/app/src/main/java/com/wireguard/crypto/Curve25519.java b/app/src/main/java/com/wireguard/crypto/Curve25519.java
index a47db7de..d279f2ae 100644
--- a/app/src/main/java/com/wireguard/crypto/Curve25519.java
+++ b/app/src/main/java/com/wireguard/crypto/Curve25519.java
@@ -5,6 +5,8 @@
 
 package com.wireguard.crypto;
 
+import android.support.annotation.Nullable;
+
 import java.util.Arrays;
 
 /**
@@ -93,7 +95,7 @@ public final class Curve25519 {
      *                   if the base point of the curve should be used.
      */
     public static void eval(final byte[] result, final int offset,
-                            final byte[] privateKey, final byte[] publicKey) {
+                            final byte[] privateKey, @Nullable final byte[] publicKey) {
         final Curve25519 state = new Curve25519();
         try {
             // Unpack the public key value.  If null, use 9 as the base point.
diff --git a/app/src/main/java/com/wireguard/util/NonNullForAll.java b/app/src/main/java/com/wireguard/util/NonNullForAll.java
new file mode 100644
index 00000000..f74cb616
--- /dev/null
+++ b/app/src/main/java/com/wireguard/util/NonNullForAll.java
@@ -0,0 +1,25 @@
+/*
+ * Copyright © 2018 Eric Kuck <eric@bluelinelabs.com>.
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package com.wireguard.util;
+
+import java.lang.annotation.Documented;
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+
+import javax.annotation.Nonnull;
+import javax.annotation.meta.TypeQualifierDefault;
+
+/**
+ * This annotation can be applied to a package, class or method to indicate that all
+ * class fields and method parameters and return values in that element are nonnull
+ * by default unless overridden.
+ */
+@Documented
+@Nonnull
+@TypeQualifierDefault({ElementType.FIELD, ElementType.METHOD, ElementType.PARAMETER})
+@Retention(RetentionPolicy.RUNTIME)
+public @interface NonNullForAll { }