diff --git a/shell/platform/android/io/flutter/embedding/android/FlutterView.java b/shell/platform/android/io/flutter/embedding/android/FlutterView.java
index cb6269756a9d6..19b4986c7efe9 100644
--- a/shell/platform/android/io/flutter/embedding/android/FlutterView.java
+++ b/shell/platform/android/io/flutter/embedding/android/FlutterView.java
@@ -878,7 +878,7 @@ public InputConnection onCreateInputConnection(@NonNull EditorInfo outAttrs) {
    * previous {@code keyCode} to generate a unicode combined character.
    */
   @Override
-  public boolean dispatchKeyEvent(KeyEvent event) {
+  public boolean dispatchKeyEvent(@NonNull KeyEvent event) {
     if (event.getAction() == KeyEvent.ACTION_DOWN && event.getRepeatCount() == 0) {
       // Tell Android to start tracking this event.
       getKeyDispatcherState().startTracking(event, this);
@@ -987,6 +987,7 @@ public AccessibilityNodeProvider getAccessibilityNodeProvider() {
    * @return The view matching the accessibility id if any.
    */
   @SuppressLint("SoonBlockedPrivateApi")
+  @Nullable
   public View findViewByAccessibilityIdTraversal(int accessibilityId) {
     if (Build.VERSION.SDK_INT < Build.VERSION_CODES.Q) {
       return findViewByAccessibilityIdRootedAtCurrentView(accessibilityId, this);
@@ -1333,7 +1334,7 @@ public void onFlutterUiNoLongerDisplayed() {
         });
   }
 
-  public void attachOverlaySurfaceToRender(FlutterImageView view) {
+  public void attachOverlaySurfaceToRender(@NonNull FlutterImageView view) {
     if (flutterEngine != null) {
       view.attachToRenderer(flutterEngine.getRenderer());
     }
@@ -1434,13 +1435,13 @@ private void sendViewportMetricsToFlutter() {
   }
 
   @Override
-  public void onProvideAutofillVirtualStructure(ViewStructure structure, int flags) {
+  public void onProvideAutofillVirtualStructure(@NonNull ViewStructure structure, int flags) {
     super.onProvideAutofillVirtualStructure(structure, flags);
     textInputPlugin.onProvideAutofillVirtualStructure(structure, flags);
   }
 
   @Override
-  public void autofill(SparseArray<AutofillValue> values) {
+  public void autofill(@NonNull SparseArray<AutofillValue> values) {
     textInputPlugin.autofill(values);
   }
 
diff --git a/shell/platform/android/io/flutter/embedding/android/KeyboardManager.java b/shell/platform/android/io/flutter/embedding/android/KeyboardManager.java
index b2a10184f6610..dba9780a2c10a 100644
--- a/shell/platform/android/io/flutter/embedding/android/KeyboardManager.java
+++ b/shell/platform/android/io/flutter/embedding/android/KeyboardManager.java
@@ -79,7 +79,9 @@ public class KeyboardManager {
    *     dispatched to.
    */
   public KeyboardManager(
-      View view, @NonNull TextInputPlugin textInputPlugin, Responder[] responders) {
+      @NonNull View view,
+      @NonNull TextInputPlugin textInputPlugin,
+      @NonNull Responder[] responders) {
     this.view = view;
     this.textInputPlugin = textInputPlugin;
     this.responders = responders;
@@ -103,7 +105,7 @@ public KeyboardManager(
    */
   interface Responder {
     interface OnKeyEventHandledCallback {
-      void onKeyEventHandled(Boolean canHandleEvent);
+      void onKeyEventHandled(boolean canHandleEvent);
     }
 
     /**
@@ -122,7 +124,7 @@ private class Callback implements OnKeyEventHandledCallback {
       boolean isCalled = false;
 
       @Override
-      public void onKeyEventHandled(Boolean canHandleEvent) {
+      public void onKeyEventHandled(boolean canHandleEvent) {
         if (isCalled) {
           throw new IllegalStateException(
               "The onKeyEventHandledCallback should be called exactly once.");
@@ -140,7 +142,7 @@ public void onKeyEventHandled(Boolean canHandleEvent) {
       this.keyEvent = keyEvent;
     }
 
-    @NonNull final KeyEvent keyEvent;
+    final KeyEvent keyEvent;
     int unrepliedCount = responders.length;
     boolean isEventHandled = false;
 
@@ -149,9 +151,9 @@ public OnKeyEventHandledCallback buildCallback() {
     }
   }
 
-  @NonNull protected final Responder[] responders;
-  @NonNull private final HashSet<KeyEvent> redispatchedEvents = new HashSet<>();
-  @NonNull private final TextInputPlugin textInputPlugin;
+  protected final Responder[] responders;
+  private final HashSet<KeyEvent> redispatchedEvents = new HashSet<>();
+  private final TextInputPlugin textInputPlugin;
   private final View view;
 
   public boolean handleEvent(@NonNull KeyEvent keyEvent) {
diff --git a/shell/platform/android/io/flutter/embedding/android/MotionEventTracker.java b/shell/platform/android/io/flutter/embedding/android/MotionEventTracker.java
index 1cd12b6e17e77..9ac225c83ae7f 100644
--- a/shell/platform/android/io/flutter/embedding/android/MotionEventTracker.java
+++ b/shell/platform/android/io/flutter/embedding/android/MotionEventTracker.java
@@ -2,6 +2,7 @@
 
 import android.util.LongSparseArray;
 import android.view.MotionEvent;
+import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import java.util.PriorityQueue;
 import java.util.concurrent.atomic.AtomicLong;
@@ -18,10 +19,12 @@ private MotionEventId(long id) {
       this.id = id;
     }
 
+    @NonNull
     public static MotionEventId from(long id) {
       return new MotionEventId(id);
     }
 
+    @NonNull
     public static MotionEventId createUnique() {
       return MotionEventId.from(ID_COUNTER.incrementAndGet());
     }
@@ -35,6 +38,7 @@ public long getId() {
   private final PriorityQueue<Long> unusedEvents;
   private static MotionEventTracker INSTANCE;
 
+  @NonNull
   public static MotionEventTracker getInstance() {
     if (INSTANCE == null) {
       INSTANCE = new MotionEventTracker();
@@ -48,7 +52,8 @@ private MotionEventTracker() {
   }
 
   /** Tracks the event and returns a unique MotionEventId identifying the event. */
-  public MotionEventId track(MotionEvent event) {
+  @NonNull
+  public MotionEventId track(@NonNull MotionEvent event) {
     MotionEventId eventId = MotionEventId.createUnique();
     eventById.put(eventId.id, MotionEvent.obtain(event));
     unusedEvents.add(eventId.id);
@@ -61,7 +66,7 @@ public MotionEventId track(MotionEvent event) {
    * popped or discarded.
    */
   @Nullable
-  public MotionEvent pop(MotionEventId eventId) {
+  public MotionEvent pop(@NonNull MotionEventId eventId) {
     // remove all the older events.
     while (!unusedEvents.isEmpty() && unusedEvents.peek() < eventId.id) {
       eventById.remove(unusedEvents.poll());
diff --git a/shell/platform/android/io/flutter/embedding/engine/deferredcomponents/PlayStoreDeferredComponentManager.java b/shell/platform/android/io/flutter/embedding/engine/deferredcomponents/PlayStoreDeferredComponentManager.java
index 156531eb011b8..989566872de04 100644
--- a/shell/platform/android/io/flutter/embedding/engine/deferredcomponents/PlayStoreDeferredComponentManager.java
+++ b/shell/platform/android/io/flutter/embedding/engine/deferredcomponents/PlayStoreDeferredComponentManager.java
@@ -66,7 +66,7 @@ public class PlayStoreDeferredComponentManager implements DeferredComponentManag
 
   private class FeatureInstallStateUpdatedListener implements SplitInstallStateUpdatedListener {
     @SuppressLint("DefaultLocale")
-    public void onStateUpdate(SplitInstallSessionState state) {
+    public void onStateUpdate(@NonNull SplitInstallSessionState state) {
       int sessionId = state.sessionId();
       if (sessionIdToName.get(sessionId) != null) {
         switch (state.status()) {
@@ -231,7 +231,7 @@ private boolean verifyJNI() {
     return true;
   }
 
-  public void setDeferredComponentChannel(DeferredComponentChannel channel) {
+  public void setDeferredComponentChannel(@NonNull DeferredComponentChannel channel) {
     this.channel = channel;
   }
 
@@ -288,7 +288,7 @@ private void initLoadingUnitMappingToComponentNames() {
     }
   }
 
-  public void installDeferredComponent(int loadingUnitId, String componentName) {
+  public void installDeferredComponent(int loadingUnitId, @Nullable String componentName) {
     String resolvedComponentName =
         componentName != null ? componentName : loadingUnitIdToComponentNames.get(loadingUnitId);
     if (resolvedComponentName == null) {
@@ -357,7 +357,9 @@ public void installDeferredComponent(int loadingUnitId, String componentName) {
             });
   }
 
-  public String getDeferredComponentInstallState(int loadingUnitId, String componentName) {
+  @NonNull
+  public String getDeferredComponentInstallState(
+      int loadingUnitId, @Nullable String componentName) {
     String resolvedComponentName =
         componentName != null ? componentName : loadingUnitIdToComponentNames.get(loadingUnitId);
     if (resolvedComponentName == null) {
@@ -375,7 +377,7 @@ public String getDeferredComponentInstallState(int loadingUnitId, String compone
     return sessionIdToState.get(sessionId);
   }
 
-  public void loadAssets(int loadingUnitId, String componentName) {
+  public void loadAssets(int loadingUnitId, @NonNull String componentName) {
     if (!verifyJNI()) {
       return;
     }
@@ -393,7 +395,7 @@ public void loadAssets(int loadingUnitId, String componentName) {
     }
   }
 
-  public void loadDartLibrary(int loadingUnitId, String componentName) {
+  public void loadDartLibrary(int loadingUnitId, @NonNull String componentName) {
     if (!verifyJNI()) {
       return;
     }
@@ -478,7 +480,7 @@ public void loadDartLibrary(int loadingUnitId, String componentName) {
         loadingUnitId, searchPaths.toArray(new String[searchPaths.size()]));
   }
 
-  public boolean uninstallDeferredComponent(int loadingUnitId, String componentName) {
+  public boolean uninstallDeferredComponent(int loadingUnitId, @Nullable String componentName) {
     String resolvedComponentName =
         componentName != null ? componentName : loadingUnitIdToComponentNames.get(loadingUnitId);
     if (resolvedComponentName == null) {
diff --git a/shell/platform/android/io/flutter/embedding/engine/plugins/shim/ShimPluginRegistry.java b/shell/platform/android/io/flutter/embedding/engine/plugins/shim/ShimPluginRegistry.java
index 671e24e0ee53c..b5db78ab35dd0 100644
--- a/shell/platform/android/io/flutter/embedding/engine/plugins/shim/ShimPluginRegistry.java
+++ b/shell/platform/android/io/flutter/embedding/engine/plugins/shim/ShimPluginRegistry.java
@@ -48,7 +48,8 @@ public ShimPluginRegistry(@NonNull FlutterEngine flutterEngine) {
   }
 
   @Override
-  public Registrar registrarFor(String pluginKey) {
+  @NonNull
+  public Registrar registrarFor(@NonNull String pluginKey) {
     Log.v(TAG, "Creating plugin Registrar for '" + pluginKey + "'");
     if (pluginMap.containsKey(pluginKey)) {
       throw new IllegalStateException("Plugin key " + pluginKey + " is already in use");
@@ -60,13 +61,13 @@ public Registrar registrarFor(String pluginKey) {
   }
 
   @Override
-  public boolean hasPlugin(String pluginKey) {
+  public boolean hasPlugin(@NonNull String pluginKey) {
     return pluginMap.containsKey(pluginKey);
   }
 
   @Override
   @SuppressWarnings("unchecked")
-  public <T> T valuePublishedByPlugin(String pluginKey) {
+  public <T> T valuePublishedByPlugin(@NonNull String pluginKey) {
     return (T) pluginMap.get(pluginKey);
   }
 
diff --git a/shell/platform/android/io/flutter/embedding/engine/renderer/SurfaceTextureWrapper.java b/shell/platform/android/io/flutter/embedding/engine/renderer/SurfaceTextureWrapper.java
index 55f183c6c6cd6..379fd3c558fc1 100644
--- a/shell/platform/android/io/flutter/embedding/engine/renderer/SurfaceTextureWrapper.java
+++ b/shell/platform/android/io/flutter/embedding/engine/renderer/SurfaceTextureWrapper.java
@@ -86,7 +86,7 @@ public void detachFromGLContext() {
 
   // Called by native.
   @SuppressWarnings("unused")
-  public void getTransformMatrix(float[] mtx) {
+  public void getTransformMatrix(@NonNull float[] mtx) {
     surfaceTexture.getTransformMatrix(mtx);
   }
 }
diff --git a/shell/platform/android/io/flutter/embedding/engine/systemchannels/LocalizationChannel.java b/shell/platform/android/io/flutter/embedding/engine/systemchannels/LocalizationChannel.java
index f060a4d89eb45..dbd94b719f074 100644
--- a/shell/platform/android/io/flutter/embedding/engine/systemchannels/LocalizationChannel.java
+++ b/shell/platform/android/io/flutter/embedding/engine/systemchannels/LocalizationChannel.java
@@ -110,6 +110,7 @@ public interface LocalizationMessageHandler {
      * The Flutter application would like to obtain the string resource of given {@code key} in
      * {@code locale}.
      */
-    String getStringResource(@NonNull String key, String locale);
+    @NonNull
+    String getStringResource(@NonNull String key, @NonNull String locale);
   }
 }
diff --git a/shell/platform/android/io/flutter/embedding/engine/systemchannels/RestorationChannel.java b/shell/platform/android/io/flutter/embedding/engine/systemchannels/RestorationChannel.java
index 7249620ecdd1d..1616bb1e93622 100644
--- a/shell/platform/android/io/flutter/embedding/engine/systemchannels/RestorationChannel.java
+++ b/shell/platform/android/io/flutter/embedding/engine/systemchannels/RestorationChannel.java
@@ -5,6 +5,7 @@
 package io.flutter.embedding.engine.systemchannels;
 
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import io.flutter.Log;
 import io.flutter.embedding.engine.dart.DartExecutor;
 import io.flutter.plugin.common.MethodCall;
@@ -72,12 +73,13 @@ public RestorationChannel(
   private boolean frameworkHasRequestedData = false;
 
   /** Obtain the most current restoration data that the framework has provided. */
+  @Nullable
   public byte[] getRestorationData() {
     return restorationData;
   }
 
   /** Set the restoration data from which the framework will restore its state. */
-  public void setRestorationData(byte[] data) {
+  public void setRestorationData(@NonNull byte[] data) {
     engineHasProvidedData = true;
     if (pendingFrameworkRestorationChannelRequest != null) {
       // If their is a pending request from the framework, answer it.
diff --git a/shell/platform/android/io/flutter/embedding/engine/systemchannels/TextInputChannel.java b/shell/platform/android/io/flutter/embedding/engine/systemchannels/TextInputChannel.java
index 4c497e05d092b..a48e073dc5f60 100644
--- a/shell/platform/android/io/flutter/embedding/engine/systemchannels/TextInputChannel.java
+++ b/shell/platform/android/io/flutter/embedding/engine/systemchannels/TextInputChannel.java
@@ -203,7 +203,7 @@ private static HashMap<Object, Object> createEditingDeltaJSON(
    */
   public void updateEditingState(
       int inputClientId,
-      String text,
+      @NonNull String text,
       int selectionStart,
       int selectionEnd,
       int composingStart,
@@ -233,7 +233,7 @@ public void updateEditingState(
   }
 
   public void updateEditingStateWithDeltas(
-      int inputClientId, ArrayList<TextEditingDelta> batchDeltas) {
+      int inputClientId, @NonNull ArrayList<TextEditingDelta> batchDeltas) {
 
     Log.v(
         TAG,
@@ -248,7 +248,7 @@ public void updateEditingStateWithDeltas(
   }
 
   public void updateEditingStateWithTag(
-      int inputClientId, HashMap<String, TextEditState> editStates) {
+      int inputClientId, @NonNull HashMap<String, TextEditState> editStates) {
     Log.v(
         TAG,
         "Sending message to update editing state for "
@@ -323,7 +323,8 @@ public void unspecifiedAction(int inputClientId) {
         Arrays.asList(inputClientId, "TextInputAction.unspecified"));
   }
 
-  public void performPrivateCommand(int inputClientId, String action, Bundle data) {
+  public void performPrivateCommand(
+      int inputClientId, @NonNull String action, @NonNull Bundle data) {
     HashMap<Object, Object> json = new HashMap<>();
     json.put("action", action);
     if (data != null) {
@@ -411,7 +412,7 @@ public interface TextInputMethodHandler {
      * @param transform a 4x4 matrix that maps the local paint coordinate system to coordinate
      *     system of the FlutterView that owns the current client.
      */
-    void setEditableSizeAndTransform(double width, double height, double[] transform);
+    void setEditableSizeAndTransform(double width, double height, @NonNull double[] transform);
 
     // TODO(mattcarroll): javadoc
     void setEditingState(@NonNull TextEditState editingState);
@@ -428,11 +429,12 @@ public interface TextInputMethodHandler {
      *     commands.
      * @param data Any data to include with the command.
      */
-    void sendAppPrivateCommand(String action, Bundle data);
+    void sendAppPrivateCommand(@NonNull String action, @NonNull Bundle data);
   }
 
   /** A text editing configuration. */
   public static class Configuration {
+    @NonNull
     public static Configuration fromJson(@NonNull JSONObject json)
         throws JSONException, NoSuchFieldException {
       final String inputActionName = json.getString("inputAction");
@@ -490,6 +492,7 @@ private static Integer inputActionFromTextInputAction(@NonNull String inputActio
     }
 
     public static class Autofill {
+      @NonNull
       public static Autofill fromJson(@NonNull JSONObject json)
           throws JSONException, NoSuchFieldException {
         final String uniqueIdentifier = json.getString("uniqueIdentifier");
@@ -725,6 +728,7 @@ static TextCapitalization fromValue(@NonNull String encodedName) throws NoSuchFi
 
   /** State of an on-going text editing session. */
   public static class TextEditState {
+    @NonNull
     public static TextEditState fromJson(@NonNull JSONObject textEditState) throws JSONException {
       return new TextEditState(
           textEditState.getString("text"),
diff --git a/shell/platform/android/io/flutter/plugin/common/JSONMessageCodec.java b/shell/platform/android/io/flutter/plugin/common/JSONMessageCodec.java
index c6bf0e668b790..b2b57a452d4f8 100644
--- a/shell/platform/android/io/flutter/plugin/common/JSONMessageCodec.java
+++ b/shell/platform/android/io/flutter/plugin/common/JSONMessageCodec.java
@@ -4,6 +4,7 @@
 
 package io.flutter.plugin.common;
 
+import androidx.annotation.Nullable;
 import java.nio.ByteBuffer;
 import org.json.JSONException;
 import org.json.JSONObject;
@@ -28,7 +29,8 @@ public final class JSONMessageCodec implements MessageCodec<Object> {
   private JSONMessageCodec() {}
 
   @Override
-  public ByteBuffer encodeMessage(Object message) {
+  @Nullable
+  public ByteBuffer encodeMessage(@Nullable Object message) {
     if (message == null) {
       return null;
     }
@@ -41,7 +43,8 @@ public ByteBuffer encodeMessage(Object message) {
   }
 
   @Override
-  public Object decodeMessage(ByteBuffer message) {
+  @Nullable
+  public Object decodeMessage(@Nullable ByteBuffer message) {
     if (message == null) {
       return null;
     }
diff --git a/shell/platform/android/io/flutter/plugin/common/JSONMethodCodec.java b/shell/platform/android/io/flutter/plugin/common/JSONMethodCodec.java
index df96af0c66b5c..3869bd5169c50 100644
--- a/shell/platform/android/io/flutter/plugin/common/JSONMethodCodec.java
+++ b/shell/platform/android/io/flutter/plugin/common/JSONMethodCodec.java
@@ -4,6 +4,8 @@
 
 package io.flutter.plugin.common;
 
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import java.nio.ByteBuffer;
 import org.json.JSONArray;
 import org.json.JSONException;
@@ -26,7 +28,8 @@ public final class JSONMethodCodec implements MethodCodec {
   private JSONMethodCodec() {}
 
   @Override
-  public ByteBuffer encodeMethodCall(MethodCall methodCall) {
+  @NonNull
+  public ByteBuffer encodeMethodCall(@NonNull MethodCall methodCall) {
     try {
       final JSONObject map = new JSONObject();
       map.put("method", methodCall.method);
@@ -38,7 +41,8 @@ public ByteBuffer encodeMethodCall(MethodCall methodCall) {
   }
 
   @Override
-  public MethodCall decodeMethodCall(ByteBuffer message) {
+  @NonNull
+  public MethodCall decodeMethodCall(@NonNull ByteBuffer message) {
     try {
       final Object json = JSONMessageCodec.INSTANCE.decodeMessage(message);
       if (json instanceof JSONObject) {
@@ -56,13 +60,15 @@ public MethodCall decodeMethodCall(ByteBuffer message) {
   }
 
   @Override
-  public ByteBuffer encodeSuccessEnvelope(Object result) {
+  @NonNull
+  public ByteBuffer encodeSuccessEnvelope(@Nullable Object result) {
     return JSONMessageCodec.INSTANCE.encodeMessage(new JSONArray().put(JSONUtil.wrap(result)));
   }
 
   @Override
+  @NonNull
   public ByteBuffer encodeErrorEnvelope(
-      String errorCode, String errorMessage, Object errorDetails) {
+      @NonNull String errorCode, @Nullable String errorMessage, @Nullable Object errorDetails) {
     return JSONMessageCodec.INSTANCE.encodeMessage(
         new JSONArray()
             .put(errorCode)
@@ -71,8 +77,12 @@ public ByteBuffer encodeErrorEnvelope(
   }
 
   @Override
+  @NonNull
   public ByteBuffer encodeErrorEnvelopeWithStacktrace(
-      String errorCode, String errorMessage, Object errorDetails, String errorStacktrace) {
+      @NonNull String errorCode,
+      @Nullable String errorMessage,
+      @Nullable Object errorDetails,
+      @Nullable String errorStacktrace) {
     return JSONMessageCodec.INSTANCE.encodeMessage(
         new JSONArray()
             .put(errorCode)
@@ -82,7 +92,8 @@ public ByteBuffer encodeErrorEnvelopeWithStacktrace(
   }
 
   @Override
-  public Object decodeEnvelope(ByteBuffer envelope) {
+  @NonNull
+  public Object decodeEnvelope(@NonNull ByteBuffer envelope) {
     try {
       final Object json = JSONMessageCodec.INSTANCE.decodeMessage(envelope);
       if (json instanceof JSONArray) {
diff --git a/shell/platform/android/io/flutter/plugin/common/JSONUtil.java b/shell/platform/android/io/flutter/plugin/common/JSONUtil.java
index bb59833b29fe4..1ee87f6fc397f 100644
--- a/shell/platform/android/io/flutter/plugin/common/JSONUtil.java
+++ b/shell/platform/android/io/flutter/plugin/common/JSONUtil.java
@@ -1,5 +1,6 @@
 package io.flutter.plugin.common;
 
+import androidx.annotation.Nullable;
 import java.lang.reflect.Array;
 import java.util.ArrayList;
 import java.util.Collection;
@@ -17,7 +18,8 @@ private JSONUtil() {}
    * Convert the Json java representation to Java objects. Particularly used for converting
    * JSONArray and JSONObject to Lists and Maps.
    */
-  public static Object unwrap(Object o) {
+  @Nullable
+  public static Object unwrap(@Nullable Object o) {
     if (JSONObject.NULL.equals(o) || o == null) {
       return null;
     }
@@ -57,7 +59,8 @@ public static Object unwrap(Object o) {
   }
 
   /** Backport of {@link JSONObject#wrap(Object)} for use on pre-KitKat systems. */
-  public static Object wrap(Object o) {
+  @Nullable
+  public static Object wrap(@Nullable Object o) {
     if (o == null) {
       return JSONObject.NULL;
     }
diff --git a/shell/platform/android/io/flutter/plugin/common/MethodCall.java b/shell/platform/android/io/flutter/plugin/common/MethodCall.java
index 8a6e51783e696..7181a548e713a 100644
--- a/shell/platform/android/io/flutter/plugin/common/MethodCall.java
+++ b/shell/platform/android/io/flutter/plugin/common/MethodCall.java
@@ -4,6 +4,7 @@
 
 package io.flutter.plugin.common;
 
+import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import io.flutter.BuildConfig;
 import java.util.Map;
@@ -27,9 +28,10 @@ public final class MethodCall {
    * Creates a {@link MethodCall} with the specified method name and arguments.
    *
    * @param method the method name String, not null.
-   * @param arguments the arguments, a value supported by the channel's message codec.
+   * @param arguments the arguments, a value supported by the channel's message codec. Possibly,
+   *     null.
    */
-  public MethodCall(String method, Object arguments) {
+  public MethodCall(@NonNull String method, @Nullable Object arguments) {
     if (BuildConfig.DEBUG && method == null) {
       throw new AssertionError("Parameter method must not be null.");
     }
@@ -44,6 +46,7 @@ public MethodCall(String method, Object arguments) {
    * @return the arguments with static type T
    */
   @SuppressWarnings("unchecked")
+  @Nullable
   public <T> T arguments() {
     return (T) arguments;
   }
@@ -62,7 +65,7 @@ public <T> T arguments() {
    */
   @SuppressWarnings("unchecked")
   @Nullable
-  public <T> T argument(String key) {
+  public <T> T argument(@NonNull String key) {
     if (arguments == null) {
       return null;
     } else if (arguments instanceof Map) {
@@ -85,7 +88,7 @@ public <T> T argument(String key) {
    * @throws ClassCastException if {@link #arguments} can be cast to neither {@link Map} nor {@link
    *     JSONObject}.
    */
-  public boolean hasArgument(String key) {
+  public boolean hasArgument(@NonNull String key) {
     if (arguments == null) {
       return false;
     } else if (arguments instanceof Map) {
diff --git a/shell/platform/android/io/flutter/plugin/common/MethodChannel.java b/shell/platform/android/io/flutter/plugin/common/MethodChannel.java
index 5e187cf94cd47..c13f82d2beb1f 100644
--- a/shell/platform/android/io/flutter/plugin/common/MethodChannel.java
+++ b/shell/platform/android/io/flutter/plugin/common/MethodChannel.java
@@ -44,7 +44,7 @@ public class MethodChannel {
    * @param messenger a {@link BinaryMessenger}.
    * @param name a channel name String.
    */
-  public MethodChannel(BinaryMessenger messenger, String name) {
+  public MethodChannel(@NonNull BinaryMessenger messenger, @NonNull String name) {
     this(messenger, name, StandardMethodCodec.INSTANCE);
   }
 
@@ -56,7 +56,8 @@ public MethodChannel(BinaryMessenger messenger, String name) {
    * @param name a channel name String.
    * @param codec a {@link MessageCodec}.
    */
-  public MethodChannel(BinaryMessenger messenger, String name, MethodCodec codec) {
+  public MethodChannel(
+      @NonNull BinaryMessenger messenger, @NonNull String name, @NonNull MethodCodec codec) {
     this(messenger, name, codec, null);
   }
 
@@ -72,9 +73,9 @@ public MethodChannel(BinaryMessenger messenger, String name, MethodCodec codec)
    *     BinaryMessenger#makeBackgroundTaskQueue()}.
    */
   public MethodChannel(
-      BinaryMessenger messenger,
-      String name,
-      MethodCodec codec,
+      @NonNull BinaryMessenger messenger,
+      @NonNull String name,
+      @NonNull MethodCodec codec,
       @Nullable BinaryMessenger.TaskQueue taskQueue) {
     if (BuildConfig.DEBUG) {
       if (messenger == null) {
@@ -114,7 +115,8 @@ public void invokeMethod(@NonNull String method, @Nullable Object arguments) {
    * @param callback a {@link Result} callback for the invocation result, or null.
    */
   @UiThread
-  public void invokeMethod(String method, @Nullable Object arguments, @Nullable Result callback) {
+  public void invokeMethod(
+      @NonNull String method, @Nullable Object arguments, @Nullable Result callback) {
     messenger.send(
         name,
         codec.encodeMethodCall(new MethodCall(method, arguments)),
@@ -212,7 +214,8 @@ public interface Result {
      *     supported by the codec. For instance, if you are using {@link StandardMessageCodec}
      *     (default), please see its documentation on what types are supported.
      */
-    void error(String errorCode, @Nullable String errorMessage, @Nullable Object errorDetails);
+    void error(
+        @NonNull String errorCode, @Nullable String errorMessage, @Nullable Object errorDetails);
 
     /** Handles a call to an unimplemented method. */
     void notImplemented();
diff --git a/shell/platform/android/io/flutter/plugin/common/MethodCodec.java b/shell/platform/android/io/flutter/plugin/common/MethodCodec.java
index f958a5307ae9c..74594ad1e69a8 100644
--- a/shell/platform/android/io/flutter/plugin/common/MethodCodec.java
+++ b/shell/platform/android/io/flutter/plugin/common/MethodCodec.java
@@ -4,6 +4,8 @@
 
 package io.flutter.plugin.common;
 
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import java.nio.ByteBuffer;
 
 /**
@@ -23,7 +25,8 @@ public interface MethodCodec {
    * @return a {@link ByteBuffer} containing the encoding between position 0 and the current
    *     position.
    */
-  ByteBuffer encodeMethodCall(MethodCall methodCall);
+  @NonNull
+  ByteBuffer encodeMethodCall(@NonNull MethodCall methodCall);
 
   /**
    * Decodes a message call from binary.
@@ -32,7 +35,8 @@ public interface MethodCodec {
    * @return a {@link MethodCall} representation of the bytes between the given buffer's current
    *     position and its limit.
    */
-  MethodCall decodeMethodCall(ByteBuffer methodCall);
+  @NonNull
+  MethodCall decodeMethodCall(@NonNull ByteBuffer methodCall);
 
   /**
    * Encodes a successful result into a binary envelope message.
@@ -41,7 +45,8 @@ public interface MethodCodec {
    * @return a {@link ByteBuffer} containing the encoding between position 0 and the current
    *     position.
    */
-  ByteBuffer encodeSuccessEnvelope(Object result);
+  @NonNull
+  ByteBuffer encodeSuccessEnvelope(@Nullable Object result);
 
   /**
    * Encodes an error result into a binary envelope message.
@@ -53,7 +58,9 @@ public interface MethodCodec {
    * @return a {@link ByteBuffer} containing the encoding between position 0 and the current
    *     position.
    */
-  ByteBuffer encodeErrorEnvelope(String errorCode, String errorMessage, Object errorDetails);
+  @NonNull
+  ByteBuffer encodeErrorEnvelope(
+      @NonNull String errorCode, @Nullable String errorMessage, @Nullable Object errorDetails);
 
   /**
    * Encodes an error result into a binary envelope message with the native stacktrace.
@@ -66,8 +73,12 @@ public interface MethodCodec {
    * @return a {@link ByteBuffer} containing the encoding between position 0 and the current
    *     position.
    */
+  @NonNull
   ByteBuffer encodeErrorEnvelopeWithStacktrace(
-      String errorCode, String errorMessage, Object errorDetails, String errorStacktrace);
+      @NonNull String errorCode,
+      @Nullable String errorMessage,
+      @Nullable Object errorDetails,
+      @Nullable String errorStacktrace);
 
   /**
    * Decodes a result envelope from binary.
@@ -76,5 +87,6 @@ ByteBuffer encodeErrorEnvelopeWithStacktrace(
    * @return the enveloped result Object.
    * @throws FlutterException if the envelope was an error envelope.
    */
-  Object decodeEnvelope(ByteBuffer envelope);
+  @NonNull
+  Object decodeEnvelope(@NonNull ByteBuffer envelope);
 }
diff --git a/shell/platform/android/io/flutter/plugin/common/PluginRegistry.java b/shell/platform/android/io/flutter/plugin/common/PluginRegistry.java
index d645e98f7edfa..29b6097933b60 100644
--- a/shell/platform/android/io/flutter/plugin/common/PluginRegistry.java
+++ b/shell/platform/android/io/flutter/plugin/common/PluginRegistry.java
@@ -7,6 +7,8 @@
 import android.app.Activity;
 import android.content.Context;
 import android.content.Intent;
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import io.flutter.embedding.engine.plugins.FlutterPlugin;
 import io.flutter.embedding.engine.plugins.activity.ActivityAware;
 import io.flutter.embedding.engine.plugins.activity.ActivityPluginBinding;
@@ -36,7 +38,8 @@ public interface PluginRegistry {
    * @deprecated See https://flutter.dev/go/android-project-migration for migration details.
    */
   @Deprecated
-  Registrar registrarFor(String pluginKey);
+  @NonNull
+  Registrar registrarFor(@NonNull String pluginKey);
 
   /**
    * Returns whether the specified plugin is known to this registry.
@@ -47,7 +50,7 @@ public interface PluginRegistry {
    * @deprecated See https://flutter.dev/go/android-project-migration for migration details.
    */
   @Deprecated
-  boolean hasPlugin(String pluginKey);
+  boolean hasPlugin(@NonNull String pluginKey);
 
   /**
    * Returns the value published by the specified plugin, if any.
@@ -63,7 +66,8 @@ public interface PluginRegistry {
    * @deprecated See https://flutter.dev/go/android-project-migration for migration details.
    */
   @Deprecated
-  <T> T valuePublishedByPlugin(String pluginKey);
+  @Nullable
+  <T> T valuePublishedByPlugin(@NonNull String pluginKey);
 
   /**
    * Receiver of registrations from a single plugin.
@@ -95,6 +99,7 @@ interface Registrar {
      * <p>For instructions on migrating a plugin from Flutter's v1 Android embedding to v2, visit
      * http://flutter.dev/go/android-plugin-migration
      */
+    @Nullable
     Activity activity();
 
     /**
@@ -107,6 +112,7 @@ interface Registrar {
      * <p>For instructions on migrating a plugin from Flutter's v1 Android embedding to v2, visit
      * http://flutter.dev/go/android-plugin-migration
      */
+    @NonNull
     Context context();
 
     /**
@@ -122,6 +128,7 @@ interface Registrar {
      * @return the current {@link #activity() Activity}, if not null, otherwise the {@link
      *     #context() Application}.
      */
+    @NonNull
     Context activeContext();
 
     /**
@@ -135,6 +142,7 @@ interface Registrar {
      * <p>For instructions on migrating a plugin from Flutter's v1 Android embedding to v2, visit
      * http://flutter.dev/go/android-plugin-migration
      */
+    @NonNull
     BinaryMessenger messenger();
 
     /**
@@ -147,6 +155,7 @@ interface Registrar {
      * <p>For instructions on migrating a plugin from Flutter's v1 Android embedding to v2, visit
      * http://flutter.dev/go/android-plugin-migration
      */
+    @NonNull
     TextureRegistry textures();
 
     /**
@@ -161,6 +170,7 @@ interface Registrar {
      * <p>For instructions on migrating a plugin from Flutter's v1 Android embedding to v2, visit
      * http://flutter.dev/go/android-plugin-migration
      */
+    @NonNull
     PlatformViewRegistry platformViewRegistry();
 
     /**
@@ -176,6 +186,7 @@ interface Registrar {
      * <p>For instructions on migrating a plugin from Flutter's v1 Android embedding to v2, visit
      * http://flutter.dev/go/android-plugin-migration
      */
+    @NonNull
     FlutterView view();
 
     /**
@@ -187,7 +198,8 @@ interface Registrar {
      * @param asset the name of the asset. The name can be hierarchical
      * @return the filename to be used with {@link android.content.res.AssetManager}
      */
-    String lookupKeyForAsset(String asset);
+    @NonNull
+    String lookupKeyForAsset(@NonNull String asset);
 
     /**
      * Returns the file name for the given asset which originates from the specified packageName.
@@ -200,7 +212,8 @@ interface Registrar {
      * @param packageName the name of the package from which the asset originates
      * @return the file name to be used with {@link android.content.res.AssetManager}
      */
-    String lookupKeyForAsset(String asset, String packageName);
+    @NonNull
+    String lookupKeyForAsset(@NonNull String asset, @NonNull String packageName);
 
     /**
      * Publishes a value associated with the plugin being registered.
@@ -222,7 +235,8 @@ interface Registrar {
      * @param value the value, possibly null.
      * @return this {@link Registrar}.
      */
-    Registrar publish(Object value);
+    @NonNull
+    Registrar publish(@Nullable Object value);
 
     /**
      * Adds a callback allowing the plugin to take part in handling incoming calls to {@code
@@ -240,7 +254,9 @@ interface Registrar {
      * @param listener a {@link RequestPermissionsResultListener} callback.
      * @return this {@link Registrar}.
      */
-    Registrar addRequestPermissionsResultListener(RequestPermissionsResultListener listener);
+    @NonNull
+    Registrar addRequestPermissionsResultListener(
+        @NonNull RequestPermissionsResultListener listener);
 
     /**
      * Adds a callback allowing the plugin to take part in handling incoming calls to {@link
@@ -256,7 +272,8 @@ interface Registrar {
      * @param listener an {@link ActivityResultListener} callback.
      * @return this {@link Registrar}.
      */
-    Registrar addActivityResultListener(ActivityResultListener listener);
+    @NonNull
+    Registrar addActivityResultListener(@NonNull ActivityResultListener listener);
 
     /**
      * Adds a callback allowing the plugin to take part in handling incoming calls to {@link
@@ -272,7 +289,8 @@ interface Registrar {
      * @param listener a {@link NewIntentListener} callback.
      * @return this {@link Registrar}.
      */
-    Registrar addNewIntentListener(NewIntentListener listener);
+    @NonNull
+    Registrar addNewIntentListener(@NonNull NewIntentListener listener);
 
     /**
      * Adds a callback allowing the plugin to take part in handling incoming calls to {@link
@@ -288,7 +306,8 @@ interface Registrar {
      * @param listener a {@link UserLeaveHintListener} callback.
      * @return this {@link Registrar}.
      */
-    Registrar addUserLeaveHintListener(UserLeaveHintListener listener);
+    @NonNull
+    Registrar addUserLeaveHintListener(@NonNull UserLeaveHintListener listener);
 
     /**
      * Adds a callback allowing the plugin to take part in handling incoming calls to {@link
@@ -312,7 +331,8 @@ interface Registrar {
      */
     // TODO(amirh): Add a line in the javadoc above that points to a Platform Views website guide
     // when one is available (but not a website API doc)
-    Registrar addViewDestroyListener(ViewDestroyListener listener);
+    @NonNull
+    Registrar addViewDestroyListener(@NonNull ViewDestroyListener listener);
   }
 
   /**
@@ -328,7 +348,8 @@ interface RequestPermissionsResultListener {
      *     {@code PackageManager.PERMISSION_GRANTED} or {@code PackageManager.PERMISSION_DENIED}.
      * @return true if the result has been handled.
      */
-    boolean onRequestPermissionsResult(int requestCode, String[] permissions, int[] grantResults);
+    boolean onRequestPermissionsResult(
+        int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults);
   }
 
   /**
@@ -345,7 +366,7 @@ interface ActivityResultListener {
      *     attached to Intent "extras").
      * @return true if the result has been handled.
      */
-    boolean onActivityResult(int requestCode, int resultCode, Intent data);
+    boolean onActivityResult(int requestCode, int resultCode, @NonNull Intent data);
   }
 
   /**
@@ -356,7 +377,7 @@ interface NewIntentListener {
      * @param intent The new intent that was started for the activity.
      * @return true if the new intent has been handled.
      */
-    boolean onNewIntent(Intent intent);
+    boolean onNewIntent(@NonNull Intent intent);
   }
 
   /**
@@ -376,7 +397,7 @@ interface UserLeaveHintListener {
    */
   @Deprecated
   interface ViewDestroyListener {
-    boolean onViewDestroy(FlutterNativeView view);
+    boolean onViewDestroy(@NonNull FlutterNativeView view);
   }
 
   /**
@@ -389,6 +410,6 @@ interface ViewDestroyListener {
    */
   @Deprecated
   interface PluginRegistrantCallback {
-    void registerWith(PluginRegistry registry);
+    void registerWith(@NonNull PluginRegistry registry);
   }
 }
diff --git a/shell/platform/android/io/flutter/plugin/common/StandardMessageCodec.java b/shell/platform/android/io/flutter/plugin/common/StandardMessageCodec.java
index 8050292174c6c..3cd1bf31cc33d 100644
--- a/shell/platform/android/io/flutter/plugin/common/StandardMessageCodec.java
+++ b/shell/platform/android/io/flutter/plugin/common/StandardMessageCodec.java
@@ -4,6 +4,8 @@
 
 package io.flutter.plugin.common;
 
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import io.flutter.BuildConfig;
 import io.flutter.Log;
 import java.io.ByteArrayOutputStream;
@@ -65,7 +67,8 @@ public class StandardMessageCodec implements MessageCodec<Object> {
   public static final StandardMessageCodec INSTANCE = new StandardMessageCodec();
 
   @Override
-  public ByteBuffer encodeMessage(Object message) {
+  @Nullable
+  public ByteBuffer encodeMessage(@Nullable Object message) {
     if (message == null) {
       return null;
     }
@@ -77,7 +80,8 @@ public ByteBuffer encodeMessage(Object message) {
   }
 
   @Override
-  public Object decodeMessage(ByteBuffer message) {
+  @Nullable
+  public Object decodeMessage(@Nullable ByteBuffer message) {
     if (message == null) {
       return null;
     }
@@ -111,7 +115,7 @@ public Object decodeMessage(ByteBuffer message) {
    * Writes an int representing a size to the specified stream. Uses an expanding code of 1 to 5
    * bytes to optimize for small values.
    */
-  protected static final void writeSize(ByteArrayOutputStream stream, int value) {
+  protected static final void writeSize(@NonNull ByteArrayOutputStream stream, int value) {
     if (BuildConfig.DEBUG && 0 > value) {
       Log.e(TAG, "Attempted to write a negative size.");
     }
@@ -127,7 +131,7 @@ protected static final void writeSize(ByteArrayOutputStream stream, int value) {
   }
 
   /** Writes the least significant two bytes of the specified int to the specified stream. */
-  protected static final void writeChar(ByteArrayOutputStream stream, int value) {
+  protected static final void writeChar(@NonNull ByteArrayOutputStream stream, int value) {
     if (LITTLE_ENDIAN) {
       stream.write(value);
       stream.write(value >>> 8);
@@ -138,7 +142,7 @@ protected static final void writeChar(ByteArrayOutputStream stream, int value) {
   }
 
   /** Writes the specified int as 4 bytes to the specified stream. */
-  protected static final void writeInt(ByteArrayOutputStream stream, int value) {
+  protected static final void writeInt(@NonNull ByteArrayOutputStream stream, int value) {
     if (LITTLE_ENDIAN) {
       stream.write(value);
       stream.write(value >>> 8);
@@ -153,7 +157,7 @@ protected static final void writeInt(ByteArrayOutputStream stream, int value) {
   }
 
   /** Writes the specified long as 8 bytes to the specified stream. */
-  protected static final void writeLong(ByteArrayOutputStream stream, long value) {
+  protected static final void writeLong(@NonNull ByteArrayOutputStream stream, long value) {
     if (LITTLE_ENDIAN) {
       stream.write((byte) value);
       stream.write((byte) (value >>> 8));
@@ -176,17 +180,18 @@ protected static final void writeLong(ByteArrayOutputStream stream, long value)
   }
 
   /** Writes the specified double as 4 bytes to the specified stream */
-  protected static final void writeFloat(ByteArrayOutputStream stream, float value) {
+  protected static final void writeFloat(@NonNull ByteArrayOutputStream stream, float value) {
     writeInt(stream, Float.floatToIntBits(value));
   }
 
   /** Writes the specified double as 8 bytes to the specified stream. */
-  protected static final void writeDouble(ByteArrayOutputStream stream, double value) {
+  protected static final void writeDouble(@NonNull ByteArrayOutputStream stream, double value) {
     writeLong(stream, Double.doubleToLongBits(value));
   }
 
   /** Writes the length and then the actual bytes of the specified array to the specified stream. */
-  protected static final void writeBytes(ByteArrayOutputStream stream, byte[] bytes) {
+  protected static final void writeBytes(
+      @NonNull ByteArrayOutputStream stream, @NonNull byte[] bytes) {
     writeSize(stream, bytes.length);
     stream.write(bytes, 0, bytes.length);
   }
@@ -196,7 +201,7 @@ protected static final void writeBytes(ByteArrayOutputStream stream, byte[] byte
    * aligned to a whole multiple of the specified alignment. An example usage with alignment = 8 is
    * to ensure doubles are word-aligned in the stream.
    */
-  protected static final void writeAlignment(ByteArrayOutputStream stream, int alignment) {
+  protected static final void writeAlignment(@NonNull ByteArrayOutputStream stream, int alignment) {
     final int mod = stream.size() % alignment;
     if (mod != 0) {
       for (int i = 0; i < alignment - mod; i++) {
@@ -212,7 +217,7 @@ protected static final void writeAlignment(ByteArrayOutputStream stream, int ali
    * <p>Subclasses can extend the codec by overriding this method, calling super for values that the
    * extension does not handle.
    */
-  protected void writeValue(ByteArrayOutputStream stream, Object value) {
+  protected void writeValue(@NonNull ByteArrayOutputStream stream, @NonNull Object value) {
     if (value == null || value.equals(null)) {
       stream.write(NULL);
     } else if (value instanceof Boolean) {
@@ -294,7 +299,7 @@ protected void writeValue(ByteArrayOutputStream stream, Object value) {
   }
 
   /** Reads an int representing a size as written by writeSize. */
-  protected static final int readSize(ByteBuffer buffer) {
+  protected static final int readSize(@NonNull ByteBuffer buffer) {
     if (!buffer.hasRemaining()) {
       throw new IllegalArgumentException("Message corrupted");
     }
@@ -309,7 +314,8 @@ protected static final int readSize(ByteBuffer buffer) {
   }
 
   /** Reads a byte array as written by writeBytes. */
-  protected static final byte[] readBytes(ByteBuffer buffer) {
+  @NonNull
+  protected static final byte[] readBytes(@NonNull ByteBuffer buffer) {
     final int length = readSize(buffer);
     final byte[] bytes = new byte[length];
     buffer.get(bytes);
@@ -317,7 +323,7 @@ protected static final byte[] readBytes(ByteBuffer buffer) {
   }
 
   /** Reads alignment padding bytes as written by writeAlignment. */
-  protected static final void readAlignment(ByteBuffer buffer, int alignment) {
+  protected static final void readAlignment(@NonNull ByteBuffer buffer, int alignment) {
     final int mod = buffer.position() % alignment;
     if (mod != 0) {
       buffer.position(buffer.position() + alignment - mod);
@@ -325,7 +331,8 @@ protected static final void readAlignment(ByteBuffer buffer, int alignment) {
   }
 
   /** Reads a value as written by writeValue. */
-  protected final Object readValue(ByteBuffer buffer) {
+  @NonNull
+  protected final Object readValue(@NonNull ByteBuffer buffer) {
     if (!buffer.hasRemaining()) {
       throw new IllegalArgumentException("Message corrupted");
     }
@@ -339,7 +346,8 @@ protected final Object readValue(ByteBuffer buffer) {
    * <p>Subclasses may extend the codec by overriding this method, calling super for types that the
    * extension does not handle.
    */
-  protected Object readValueOfType(byte type, ByteBuffer buffer) {
+  @Nullable
+  protected Object readValueOfType(byte type, @NonNull ByteBuffer buffer) {
     final Object result;
     switch (type) {
       case NULL:
diff --git a/shell/platform/android/io/flutter/plugin/common/StandardMethodCodec.java b/shell/platform/android/io/flutter/plugin/common/StandardMethodCodec.java
index 7ef509185e27f..a2e8b211c416f 100644
--- a/shell/platform/android/io/flutter/plugin/common/StandardMethodCodec.java
+++ b/shell/platform/android/io/flutter/plugin/common/StandardMethodCodec.java
@@ -4,6 +4,7 @@
 
 package io.flutter.plugin.common;
 
+import androidx.annotation.NonNull;
 import io.flutter.plugin.common.StandardMessageCodec.ExposedByteArrayOutputStream;
 import java.io.PrintWriter;
 import java.io.StringWriter;
@@ -27,12 +28,13 @@ public final class StandardMethodCodec implements MethodCodec {
   private final StandardMessageCodec messageCodec;
 
   /** Creates a new method codec based on the specified message codec. */
-  public StandardMethodCodec(StandardMessageCodec messageCodec) {
+  public StandardMethodCodec(@NonNull StandardMessageCodec messageCodec) {
     this.messageCodec = messageCodec;
   }
 
   @Override
-  public ByteBuffer encodeMethodCall(MethodCall methodCall) {
+  @NonNull
+  public ByteBuffer encodeMethodCall(@NonNull MethodCall methodCall) {
     final ExposedByteArrayOutputStream stream = new ExposedByteArrayOutputStream();
     messageCodec.writeValue(stream, methodCall.method);
     messageCodec.writeValue(stream, methodCall.arguments);
@@ -42,7 +44,8 @@ public ByteBuffer encodeMethodCall(MethodCall methodCall) {
   }
 
   @Override
-  public MethodCall decodeMethodCall(ByteBuffer methodCall) {
+  @NonNull
+  public MethodCall decodeMethodCall(@NonNull ByteBuffer methodCall) {
     methodCall.order(ByteOrder.nativeOrder());
     final Object method = messageCodec.readValue(methodCall);
     final Object arguments = messageCodec.readValue(methodCall);
@@ -53,7 +56,8 @@ public MethodCall decodeMethodCall(ByteBuffer methodCall) {
   }
 
   @Override
-  public ByteBuffer encodeSuccessEnvelope(Object result) {
+  @NonNull
+  public ByteBuffer encodeSuccessEnvelope(@NonNull Object result) {
     final ExposedByteArrayOutputStream stream = new ExposedByteArrayOutputStream();
     stream.write(0);
     messageCodec.writeValue(stream, result);
@@ -63,8 +67,9 @@ public ByteBuffer encodeSuccessEnvelope(Object result) {
   }
 
   @Override
+  @NonNull
   public ByteBuffer encodeErrorEnvelope(
-      String errorCode, String errorMessage, Object errorDetails) {
+      @NonNull String errorCode, @NonNull String errorMessage, @NonNull Object errorDetails) {
     final ExposedByteArrayOutputStream stream = new ExposedByteArrayOutputStream();
     stream.write(1);
     messageCodec.writeValue(stream, errorCode);
@@ -80,8 +85,12 @@ public ByteBuffer encodeErrorEnvelope(
   }
 
   @Override
+  @NonNull
   public ByteBuffer encodeErrorEnvelopeWithStacktrace(
-      String errorCode, String errorMessage, Object errorDetails, String errorStacktrace) {
+      @NonNull String errorCode,
+      @NonNull String errorMessage,
+      @NonNull Object errorDetails,
+      @NonNull String errorStacktrace) {
     final ExposedByteArrayOutputStream stream = new ExposedByteArrayOutputStream();
     stream.write(1);
     messageCodec.writeValue(stream, errorCode);
@@ -98,7 +107,8 @@ public ByteBuffer encodeErrorEnvelopeWithStacktrace(
   }
 
   @Override
-  public Object decodeEnvelope(ByteBuffer envelope) {
+  @NonNull
+  public Object decodeEnvelope(@NonNull ByteBuffer envelope) {
     envelope.order(ByteOrder.nativeOrder());
     final byte flag = envelope.get();
     switch (flag) {
@@ -125,7 +135,8 @@ public Object decodeEnvelope(ByteBuffer envelope) {
     throw new IllegalArgumentException("Envelope corrupted");
   }
 
-  private static String getStackTrace(Throwable t) {
+  @NonNull
+  private static String getStackTrace(@NonNull Throwable t) {
     Writer result = new StringWriter();
     t.printStackTrace(new PrintWriter(result));
     return result.toString();
diff --git a/shell/platform/android/io/flutter/plugin/common/StringCodec.java b/shell/platform/android/io/flutter/plugin/common/StringCodec.java
index dfcdbe68bd0fc..3cf17793949ba 100644
--- a/shell/platform/android/io/flutter/plugin/common/StringCodec.java
+++ b/shell/platform/android/io/flutter/plugin/common/StringCodec.java
@@ -4,6 +4,7 @@
 
 package io.flutter.plugin.common;
 
+import androidx.annotation.Nullable;
 import java.nio.ByteBuffer;
 import java.nio.charset.Charset;
 
@@ -21,7 +22,8 @@ public final class StringCodec implements MessageCodec<String> {
   private StringCodec() {}
 
   @Override
-  public ByteBuffer encodeMessage(String message) {
+  @Nullable
+  public ByteBuffer encodeMessage(@Nullable String message) {
     if (message == null) {
       return null;
     }
@@ -33,7 +35,8 @@ public ByteBuffer encodeMessage(String message) {
   }
 
   @Override
-  public String decodeMessage(ByteBuffer message) {
+  @Nullable
+  public String decodeMessage(@Nullable ByteBuffer message) {
     if (message == null) {
       return null;
     }
diff --git a/shell/platform/android/io/flutter/plugin/editing/TextEditingDelta.java b/shell/platform/android/io/flutter/plugin/editing/TextEditingDelta.java
index c5d2bfc2902b7..8681e23c80678 100644
--- a/shell/platform/android/io/flutter/plugin/editing/TextEditingDelta.java
+++ b/shell/platform/android/io/flutter/plugin/editing/TextEditingDelta.java
@@ -4,6 +4,7 @@
 
 package io.flutter.plugin.editing;
 
+import androidx.annotation.NonNull;
 import androidx.annotation.VisibleForTesting;
 import io.flutter.Log;
 import org.json.JSONException;
@@ -12,8 +13,8 @@
 /// A representation of the change that occured to an editing state, along with the resulting
 /// composing and selection regions.
 public final class TextEditingDelta {
-  private CharSequence oldText;
-  private CharSequence deltaText;
+  private @NonNull CharSequence oldText;
+  private @NonNull CharSequence deltaText;
   private int deltaStart;
   private int deltaEnd;
   private int newSelectionStart;
@@ -24,10 +25,10 @@ public final class TextEditingDelta {
   private static final String TAG = "TextEditingDelta";
 
   public TextEditingDelta(
-      CharSequence oldEditable,
+      @NonNull CharSequence oldEditable,
       int replacementDestinationStart,
       int replacementDestinationEnd,
-      CharSequence replacementSource,
+      @NonNull CharSequence replacementSource,
       int selectionStart,
       int selectionEnd,
       int composingStart,
@@ -46,7 +47,7 @@ public TextEditingDelta(
 
   // Non text update delta constructor.
   public TextEditingDelta(
-      CharSequence oldText,
+      @NonNull CharSequence oldText,
       int selectionStart,
       int selectionEnd,
       int composingStart,
@@ -60,11 +61,13 @@ public TextEditingDelta(
   }
 
   @VisibleForTesting
+  @NonNull
   public CharSequence getOldText() {
     return oldText;
   }
 
   @VisibleForTesting
+  @NonNull
   public CharSequence getDeltaText() {
     return deltaText;
   }
@@ -99,13 +102,15 @@ public int getNewComposingEnd() {
     return newComposingEnd;
   }
 
-  private void setDeltas(CharSequence oldText, CharSequence newText, int newStart, int newExtent) {
+  private void setDeltas(
+      @NonNull CharSequence oldText, @NonNull CharSequence newText, int newStart, int newExtent) {
     this.oldText = oldText;
     deltaText = newText;
     deltaStart = newStart;
     deltaEnd = newExtent;
   }
 
+  @NonNull
   public JSONObject toJSON() {
     JSONObject delta = new JSONObject();
 
diff --git a/shell/platform/android/io/flutter/plugin/editing/TextInputPlugin.java b/shell/platform/android/io/flutter/plugin/editing/TextInputPlugin.java
index cfd57ef7a26ea..70658ee934493 100644
--- a/shell/platform/android/io/flutter/plugin/editing/TextInputPlugin.java
+++ b/shell/platform/android/io/flutter/plugin/editing/TextInputPlugin.java
@@ -56,7 +56,7 @@ public class TextInputPlugin implements ListenableEditingState.EditingStateWatch
 
   @SuppressLint("NewApi")
   public TextInputPlugin(
-      View view,
+      @NonNull View view,
       @NonNull TextInputChannel textInputChannel,
       @NonNull PlatformViewsController platformViewsController) {
     mView = view;
@@ -251,8 +251,9 @@ private static int inputTypeFromTextInputType(
     return textType;
   }
 
+  @Nullable
   public InputConnection createInputConnection(
-      View view, KeyboardManager keyboardManager, EditorInfo outAttrs) {
+      @NonNull View view, @NonNull KeyboardManager keyboardManager, @NonNull EditorInfo outAttrs) {
     if (inputTarget.type == InputTarget.Type.NO_TARGET) {
       lastInputConnection = null;
       return null;
@@ -325,7 +326,7 @@ public void clearPlatformViewClient(int platformViewId) {
     }
   }
 
-  public void sendTextInputAppPrivateCommand(String action, Bundle data) {
+  public void sendTextInputAppPrivateCommand(@NonNull String action, @NonNull Bundle data) {
     mImm.sendAppPrivateCommand(mView, action, data);
   }
 
@@ -506,7 +507,7 @@ public InputTarget(@NonNull Type type, int id) {
   }
 
   // -------- Start: KeyboardManager Synchronous Responder -------
-  public boolean handleKeyEvent(KeyEvent keyEvent) {
+  public boolean handleKeyEvent(@NonNull KeyEvent keyEvent) {
     if (!getInputMethodManager().isAcceptingText() || lastInputConnection == null) {
       return false;
     }
@@ -664,7 +665,7 @@ private void updateAutofillConfigurationIfNeeded(TextInputChannel.Configuration
     }
   }
 
-  public void onProvideAutofillVirtualStructure(ViewStructure structure, int flags) {
+  public void onProvideAutofillVirtualStructure(@NonNull ViewStructure structure, int flags) {
     if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O || !needsAutofill()) {
       return;
     }
@@ -708,7 +709,7 @@ public void onProvideAutofillVirtualStructure(ViewStructure structure, int flags
     }
   }
 
-  public void autofill(SparseArray<AutofillValue> values) {
+  public void autofill(@NonNull SparseArray<AutofillValue> values) {
     if (Build.VERSION.SDK_INT < Build.VERSION_CODES.O) {
       return;
     }
diff --git a/shell/platform/android/io/flutter/plugin/localization/LocalizationPlugin.java b/shell/platform/android/io/flutter/plugin/localization/LocalizationPlugin.java
index 66362931271bf..6d7970a5fcebc 100644
--- a/shell/platform/android/io/flutter/plugin/localization/LocalizationPlugin.java
+++ b/shell/platform/android/io/flutter/plugin/localization/LocalizationPlugin.java
@@ -82,7 +82,8 @@ public LocalizationPlugin(
    * <p>FlutterEngine must be non-null when this method is invoked.
    */
   @SuppressWarnings("deprecation")
-  public Locale resolveNativeLocale(List<Locale> supportedLocales) {
+  @Nullable
+  public Locale resolveNativeLocale(@Nullable List<Locale> supportedLocales) {
     if (supportedLocales == null || supportedLocales.isEmpty()) {
       return null;
     }
@@ -188,7 +189,8 @@ public void sendLocalesToFlutter(@NonNull Configuration config) {
   }
 
   @VisibleForTesting
-  public static Locale localeFromString(String localeString) {
+  @NonNull
+  public static Locale localeFromString(@NonNull String localeString) {
     // Use Locale.forLanguageTag if available (API 21+).
     if (false && Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.LOLLIPOP) {
       return Locale.forLanguageTag(localeString);
diff --git a/shell/platform/android/io/flutter/plugin/mouse/MouseCursorPlugin.java b/shell/platform/android/io/flutter/plugin/mouse/MouseCursorPlugin.java
index 0daa4959d67f6..f9c3a8e6f76f9 100644
--- a/shell/platform/android/io/flutter/plugin/mouse/MouseCursorPlugin.java
+++ b/shell/platform/android/io/flutter/plugin/mouse/MouseCursorPlugin.java
@@ -121,6 +121,7 @@ public interface MouseCursorViewDelegate {
      * <p>This is typically implemented by calling {@link android.view.PointerIcon#getSystemIcon}
      * with the context associated with this view.
      */
+    @NonNull
     public PointerIcon getSystemPointerIcon(int type);
 
     /**
diff --git a/shell/platform/android/io/flutter/plugin/platform/PlatformPlugin.java b/shell/platform/android/io/flutter/plugin/platform/PlatformPlugin.java
index 59733b29bd0b0..a1d38ba0720db 100644
--- a/shell/platform/android/io/flutter/plugin/platform/PlatformPlugin.java
+++ b/shell/platform/android/io/flutter/plugin/platform/PlatformPlugin.java
@@ -130,12 +130,14 @@ public boolean clipboardHasStrings() {
         }
       };
 
-  public PlatformPlugin(Activity activity, PlatformChannel platformChannel) {
+  public PlatformPlugin(@NonNull Activity activity, @NonNull PlatformChannel platformChannel) {
     this(activity, platformChannel, null);
   }
 
   public PlatformPlugin(
-      Activity activity, PlatformChannel platformChannel, PlatformPluginDelegate delegate) {
+      @NonNull Activity activity,
+      @NonNull PlatformChannel platformChannel,
+      @NonNull PlatformPluginDelegate delegate) {
     this.activity = activity;
     this.platformChannel = platformChannel;
     this.platformChannel.setPlatformMessageHandler(mPlatformMessageHandler);
@@ -153,7 +155,7 @@ public void destroy() {
     this.platformChannel.setPlatformMessageHandler(null);
   }
 
-  private void playSystemSound(PlatformChannel.SoundType soundType) {
+  private void playSystemSound(@NonNull PlatformChannel.SoundType soundType) {
     if (soundType == PlatformChannel.SoundType.CLICK) {
       View view = activity.getWindow().getDecorView();
       view.playSoundEffect(SoundEffectConstants.CLICK);
@@ -161,7 +163,8 @@ private void playSystemSound(PlatformChannel.SoundType soundType) {
   }
 
   @VisibleForTesting
-  /* package */ void vibrateHapticFeedback(PlatformChannel.HapticFeedbackType feedbackType) {
+  /* package */ void vibrateHapticFeedback(
+      @NonNull PlatformChannel.HapticFeedbackType feedbackType) {
     View view = activity.getWindow().getDecorView();
     switch (feedbackType) {
       case STANDARD:
diff --git a/shell/platform/android/io/flutter/plugin/platform/PlatformView.java b/shell/platform/android/io/flutter/plugin/platform/PlatformView.java
index 85ed3c40e8c2e..2c563ccac937b 100644
--- a/shell/platform/android/io/flutter/plugin/platform/PlatformView.java
+++ b/shell/platform/android/io/flutter/plugin/platform/PlatformView.java
@@ -7,10 +7,12 @@
 import android.annotation.SuppressLint;
 import android.view.View;
 import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 
 /** A handle to an Android view to be embedded in the Flutter hierarchy. */
 public interface PlatformView {
   /** Returns the Android view to be embedded in the Flutter hierarchy. */
+  @Nullable
   View getView();
 
   /**
diff --git a/shell/platform/android/io/flutter/plugin/platform/PlatformViewFactory.java b/shell/platform/android/io/flutter/plugin/platform/PlatformViewFactory.java
index 5144a639694f0..936f9fabeca5b 100644
--- a/shell/platform/android/io/flutter/plugin/platform/PlatformViewFactory.java
+++ b/shell/platform/android/io/flutter/plugin/platform/PlatformViewFactory.java
@@ -5,13 +5,15 @@
 package io.flutter.plugin.platform;
 
 import android.content.Context;
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import io.flutter.plugin.common.MessageCodec;
 
 public abstract class PlatformViewFactory {
   private final MessageCodec<Object> createArgsCodec;
 
   /** @param createArgsCodec the codec used to decode the args parameter of {@link #create}. */
-  public PlatformViewFactory(MessageCodec<Object> createArgsCodec) {
+  public PlatformViewFactory(@Nullable MessageCodec<Object> createArgsCodec) {
     this.createArgsCodec = createArgsCodec;
   }
 
@@ -25,9 +27,11 @@ public PlatformViewFactory(MessageCodec<Object> createArgsCodec) {
    *     createArgsCodec argument passed to the constructor. This is null if createArgsCodec was
    *     null, or no arguments were sent from the Flutter app.
    */
-  public abstract PlatformView create(Context context, int viewId, Object args);
+  @NonNull
+  public abstract PlatformView create(@Nullable Context context, int viewId, @Nullable Object args);
 
   /** Returns the codec to be used for decoding the args parameter of {@link #create}. */
+  @Nullable
   public final MessageCodec<Object> getCreateArgsCodec() {
     return createArgsCodec;
   }
diff --git a/shell/platform/android/io/flutter/plugin/platform/PlatformViewRegistry.java b/shell/platform/android/io/flutter/plugin/platform/PlatformViewRegistry.java
index e03a771cf6637..028b3b1d2eb3f 100644
--- a/shell/platform/android/io/flutter/plugin/platform/PlatformViewRegistry.java
+++ b/shell/platform/android/io/flutter/plugin/platform/PlatformViewRegistry.java
@@ -4,6 +4,8 @@
 
 package io.flutter.plugin.platform;
 
+import androidx.annotation.NonNull;
+
 /**
  * Registry for platform view factories.
  *
@@ -18,5 +20,5 @@ public interface PlatformViewRegistry {
    * @param factory factory for creating platform views of the specified type.
    * @return true if succeeded, false if a factory is already registered for viewTypeId.
    */
-  boolean registerViewFactory(String viewTypeId, PlatformViewFactory factory);
+  boolean registerViewFactory(@NonNull String viewTypeId, @NonNull PlatformViewFactory factory);
 }
diff --git a/shell/platform/android/io/flutter/plugin/platform/PlatformViewsAccessibilityDelegate.java b/shell/platform/android/io/flutter/plugin/platform/PlatformViewsAccessibilityDelegate.java
index 0ab99bfe1fc66..968dda33f1ee8 100644
--- a/shell/platform/android/io/flutter/plugin/platform/PlatformViewsAccessibilityDelegate.java
+++ b/shell/platform/android/io/flutter/plugin/platform/PlatformViewsAccessibilityDelegate.java
@@ -5,6 +5,7 @@
 package io.flutter.plugin.platform;
 
 import android.view.View;
+import androidx.annotation.NonNull;
 import androidx.annotation.Nullable;
 import io.flutter.view.AccessibilityBridge;
 
@@ -23,7 +24,7 @@ public interface PlatformViewsAccessibilityDelegate {
    * <p>Accessibility events originating in platform views belonging to this delegate will be
    * delegated to this accessibility bridge.
    */
-  void attachAccessibilityBridge(AccessibilityBridge accessibilityBridge);
+  void attachAccessibilityBridge(@NonNull AccessibilityBridge accessibilityBridge);
 
   /**
    * Detaches the current accessibility bridge.
diff --git a/shell/platform/android/io/flutter/plugin/platform/PlatformViewsController.java b/shell/platform/android/io/flutter/plugin/platform/PlatformViewsController.java
index 063882fced75f..3d9e86d749557 100644
--- a/shell/platform/android/io/flutter/plugin/platform/PlatformViewsController.java
+++ b/shell/platform/android/io/flutter/plugin/platform/PlatformViewsController.java
@@ -449,7 +449,9 @@ public PlatformViewsController() {
    * @param dartExecutor The dart execution context, which is used to set up a system channel.
    */
   public void attach(
-      Context context, TextureRegistry textureRegistry, @NonNull DartExecutor dartExecutor) {
+      @Nullable Context context,
+      @NonNull TextureRegistry textureRegistry,
+      @NonNull DartExecutor dartExecutor) {
     if (this.context != null) {
       throw new AssertionError(
           "A PlatformViewsController can only be attached to a single output target.\n"
@@ -516,7 +518,7 @@ public void detachFromView() {
   }
 
   @Override
-  public void attachAccessibilityBridge(AccessibilityBridge accessibilityBridge) {
+  public void attachAccessibilityBridge(@NonNull AccessibilityBridge accessibilityBridge) {
     accessibilityEventsDelegate.setAccessibilityBridge(accessibilityBridge);
   }
 
@@ -534,7 +536,7 @@ public void detachAccessibilityBridge() {
    * <p>A platform views controller should be attached to a text input plugin whenever it is
    * possible for the Flutter framework to receive text input.
    */
-  public void attachTextInputPlugin(TextInputPlugin textInputPlugin) {
+  public void attachTextInputPlugin(@NonNull TextInputPlugin textInputPlugin) {
     this.textInputPlugin = textInputPlugin;
   }
 
@@ -568,6 +570,7 @@ public void onPreEngineRestart() {
   }
 
   @Override
+  @Nullable
   public View getPlatformViewById(int viewId) {
     final PlatformView platformView = platformViews.get(viewId);
     if (platformView == null) {
@@ -692,7 +695,7 @@ void initializePlatformViewIfNeeded(int viewId) {
     flutterView.addView(parentView);
   }
 
-  public void attachToFlutterRenderer(FlutterRenderer flutterRenderer) {
+  public void attachToFlutterRenderer(@NonNull FlutterRenderer flutterRenderer) {
     androidTouchProcessor = new AndroidTouchProcessor(flutterRenderer, /*trackMotionEvents=*/ true);
   }
 
@@ -717,7 +720,7 @@ public void onDisplayPlatformView(
       int height,
       int viewWidth,
       int viewHeight,
-      FlutterMutatorsStack mutatorsStack) {
+      @NonNull FlutterMutatorsStack mutatorsStack) {
     initializeRootImageViewIfNeeded();
     initializePlatformViewIfNeeded(viewId);
 
@@ -856,6 +859,7 @@ private void finishFrame(boolean isFrameRenderedUsingImageReaders) {
    */
   @VisibleForTesting
   @TargetApi(19)
+  @NonNull
   public FlutterOverlaySurface createOverlaySurface(@NonNull FlutterImageView imageView) {
     final int id = nextOverlayLayerId++;
     overlayLayerViews.put(id, imageView);
@@ -870,6 +874,7 @@ public FlutterOverlaySurface createOverlaySurface(@NonNull FlutterImageView imag
    * <p>This member is not intended for public use, and is only visible for testing.
    */
   @TargetApi(19)
+  @NonNull
   public FlutterOverlaySurface createOverlaySurface() {
     // Overlay surfaces have the same size as the background surface.
     //
diff --git a/shell/platform/android/io/flutter/util/PathUtils.java b/shell/platform/android/io/flutter/util/PathUtils.java
index 1b4d36eb96529..5f3f7bd6845e4 100644
--- a/shell/platform/android/io/flutter/util/PathUtils.java
+++ b/shell/platform/android/io/flutter/util/PathUtils.java
@@ -6,10 +6,12 @@
 
 import android.content.Context;
 import android.os.Build;
+import androidx.annotation.NonNull;
 import java.io.File;
 
 public final class PathUtils {
-  public static String getFilesDir(Context applicationContext) {
+  @NonNull
+  public static String getFilesDir(@NonNull Context applicationContext) {
     File filesDir = applicationContext.getFilesDir();
     if (filesDir == null) {
       filesDir = new File(getDataDirPath(applicationContext), "files");
@@ -17,7 +19,8 @@ public static String getFilesDir(Context applicationContext) {
     return filesDir.getPath();
   }
 
-  public static String getDataDirectory(Context applicationContext) {
+  @NonNull
+  public static String getDataDirectory(@NonNull Context applicationContext) {
     final String name = "flutter";
     File flutterDir = applicationContext.getDir(name, Context.MODE_PRIVATE);
     if (flutterDir == null) {
@@ -26,7 +29,8 @@ public static String getDataDirectory(Context applicationContext) {
     return flutterDir.getPath();
   }
 
-  public static String getCacheDirectory(Context applicationContext) {
+  @NonNull
+  public static String getCacheDirectory(@NonNull Context applicationContext) {
     File cacheDir;
     if (Build.VERSION.SDK_INT >= 21) {
       cacheDir = applicationContext.getCodeCacheDir();
diff --git a/shell/platform/android/io/flutter/util/ViewUtils.java b/shell/platform/android/io/flutter/util/ViewUtils.java
index bac41ac7c06ca..95ea8fa855437 100644
--- a/shell/platform/android/io/flutter/util/ViewUtils.java
+++ b/shell/platform/android/io/flutter/util/ViewUtils.java
@@ -19,7 +19,8 @@ public final class ViewUtils {
    * <p>This method will recursively traverse up the context chain if it is a {@link ContextWrapper}
    * until it finds the first instance of the base context that is an {@link Activity}.
    */
-  public static Activity getActivity(Context context) {
+  @Nullable
+  public static Activity getActivity(@Nullable Context context) {
     if (context == null) {
       return null;
     }
diff --git a/shell/platform/android/io/flutter/view/FlutterView.java b/shell/platform/android/io/flutter/view/FlutterView.java
index beb15c38c0a8f..f47b8da5bde00 100644
--- a/shell/platform/android/io/flutter/view/FlutterView.java
+++ b/shell/platform/android/io/flutter/view/FlutterView.java
@@ -846,13 +846,16 @@ public void send(String channel, ByteBuffer message, BinaryReply callback) {
 
   @Override
   @UiThread
-  public void setMessageHandler(String channel, BinaryMessageHandler handler) {
+  public void setMessageHandler(@NonNull String channel, @NonNull BinaryMessageHandler handler) {
     mNativeView.setMessageHandler(channel, handler);
   }
 
   @Override
   @UiThread
-  public void setMessageHandler(String channel, BinaryMessageHandler handler, TaskQueue taskQueue) {
+  public void setMessageHandler(
+      @NonNull String channel,
+      @NonNull BinaryMessageHandler handler,
+      @NonNull TaskQueue taskQueue) {
     mNativeView.setMessageHandler(channel, handler, taskQueue);
   }
 
@@ -862,12 +865,14 @@ public interface FirstFrameListener {
   }
 
   @Override
+  @NonNull
   public TextureRegistry.SurfaceTextureEntry createSurfaceTexture() {
     final SurfaceTexture surfaceTexture = new SurfaceTexture(0);
     return registerSurfaceTexture(surfaceTexture);
   }
 
   @Override
+  @NonNull
   public TextureRegistry.SurfaceTextureEntry registerSurfaceTexture(
       @NonNull SurfaceTexture surfaceTexture) {
     surfaceTexture.detachFromGLContext();
diff --git a/shell/platform/android/io/flutter/view/TextureRegistry.java b/shell/platform/android/io/flutter/view/TextureRegistry.java
index 6af82ce915fcc..1155c4854bf66 100644
--- a/shell/platform/android/io/flutter/view/TextureRegistry.java
+++ b/shell/platform/android/io/flutter/view/TextureRegistry.java
@@ -19,6 +19,7 @@ public interface TextureRegistry {
    *
    * @return A SurfaceTextureEntry.
    */
+  @NonNull
   SurfaceTextureEntry createSurfaceTexture();
 
   /**
@@ -26,11 +27,13 @@ public interface TextureRegistry {
    *
    * @return A SurfaceTextureEntry.
    */
+  @NonNull
   SurfaceTextureEntry registerSurfaceTexture(@NonNull SurfaceTexture surfaceTexture);
 
   /** A registry entry for a managed SurfaceTexture. */
   interface SurfaceTextureEntry {
     /** @return The managed SurfaceTexture. */
+    @NonNull
     SurfaceTexture surfaceTexture();
 
     /** @return The identity of this SurfaceTexture. */
diff --git a/shell/platform/android/io/flutter/view/VsyncWaiter.java b/shell/platform/android/io/flutter/view/VsyncWaiter.java
index f65d6d569b088..c5021460da89b 100644
--- a/shell/platform/android/io/flutter/view/VsyncWaiter.java
+++ b/shell/platform/android/io/flutter/view/VsyncWaiter.java
@@ -49,7 +49,7 @@ public void onDisplayChanged(int displayId) {
   private FlutterJNI flutterJNI;
 
   @NonNull
-  public static VsyncWaiter getInstance(float fps, FlutterJNI flutterJNI) {
+  public static VsyncWaiter getInstance(float fps, @NonNull FlutterJNI flutterJNI) {
     if (instance == null) {
       instance = new VsyncWaiter(flutterJNI);
     }
@@ -60,7 +60,8 @@ public static VsyncWaiter getInstance(float fps, FlutterJNI flutterJNI) {
 
   @TargetApi(17)
   @NonNull
-  public static VsyncWaiter getInstance(DisplayManager displayManager, FlutterJNI flutterJNI) {
+  public static VsyncWaiter getInstance(
+      @NonNull DisplayManager displayManager, @NonNull FlutterJNI flutterJNI) {
     if (instance == null) {
       instance = new VsyncWaiter(flutterJNI);
     }
@@ -103,7 +104,7 @@ public void doFrame(long frameTimeNanos) {
         }
       };
 
-  private VsyncWaiter(FlutterJNI flutterJNI) {
+  private VsyncWaiter(@NonNull FlutterJNI flutterJNI) {
     this.flutterJNI = flutterJNI;
   }
 
diff --git a/shell/platform/android/test/io/flutter/TestUtils.java b/shell/platform/android/test/io/flutter/TestUtils.java
index ae2e79eda1878..907ced48f300c 100644
--- a/shell/platform/android/test/io/flutter/TestUtils.java
+++ b/shell/platform/android/test/io/flutter/TestUtils.java
@@ -8,6 +8,7 @@
 
 import android.content.res.Configuration;
 import android.os.Build;
+import androidx.annotation.NonNull;
 import java.lang.reflect.Field;
 import java.lang.reflect.Modifier;
 import java.util.Locale;
@@ -29,7 +30,7 @@ public static void setApiVersion(int apiVersion) {
     }
   }
 
-  public static void setLegacyLocale(Configuration config, Locale locale) {
+  public static void setLegacyLocale(@NonNull Configuration config, @NonNull Locale locale) {
     try {
       Field field = config.getClass().getField("locale");
       field.setAccessible(true);
diff --git a/shell/platform/android/test/io/flutter/embedding/android/RobolectricFlutterActivity.java b/shell/platform/android/test/io/flutter/embedding/android/RobolectricFlutterActivity.java
index 557d1e89d42b4..938c81a85d6db 100644
--- a/shell/platform/android/test/io/flutter/embedding/android/RobolectricFlutterActivity.java
+++ b/shell/platform/android/test/io/flutter/embedding/android/RobolectricFlutterActivity.java
@@ -1,6 +1,7 @@
 package io.flutter.embedding.android;
 
 import android.content.Intent;
+import androidx.annotation.NonNull;
 import org.robolectric.Robolectric;
 import org.robolectric.android.controller.ActivityController;
 
@@ -14,7 +15,8 @@ public class RobolectricFlutterActivity {
    * Creates a {@code FlutterActivity} that is controlled by Robolectric, which otherwise can not be
    * done in a test outside of the io.flutter.embedding.android package.
    */
-  public static FlutterActivity createFlutterActivity(Intent intent) {
+  @NonNull
+  public static FlutterActivity createFlutterActivity(@NonNull Intent intent) {
     ActivityController<FlutterActivity> activityController =
         Robolectric.buildActivity(FlutterActivity.class, intent);
     FlutterActivity flutterActivity = activityController.get();
@@ -26,8 +28,9 @@ public static FlutterActivity createFlutterActivity(Intent intent) {
    * Returns a given {@code FlutterActivity}'s {@code BackgroundMode} for use by tests that do not
    * sit in the {@code io.flutter.embedding.android} package.
    */
+  @NonNull
   public static FlutterActivityLaunchConfigs.BackgroundMode getBackgroundMode(
-      FlutterActivity activity) {
+      @NonNull FlutterActivity activity) {
     return activity.getBackgroundMode();
   }
 }
diff --git a/shell/platform/android/test/io/flutter/embedding/android/SplashShadowResources.java b/shell/platform/android/test/io/flutter/embedding/android/SplashShadowResources.java
index 2747092c836f8..e6cd8b6b6661e 100644
--- a/shell/platform/android/test/io/flutter/embedding/android/SplashShadowResources.java
+++ b/shell/platform/android/test/io/flutter/embedding/android/SplashShadowResources.java
@@ -4,6 +4,7 @@
 import android.graphics.Color;
 import android.graphics.drawable.ColorDrawable;
 import android.graphics.drawable.Drawable;
+import androidx.annotation.NonNull;
 import org.robolectric.annotation.Implements;
 import org.robolectric.annotation.RealObject;
 import org.robolectric.shadow.api.Shadow;
@@ -16,7 +17,8 @@ public class SplashShadowResources {
   public static final int THEMED_SPLASH_DRAWABLE_ID = 212121;
 
   // All other getDrawable() calls, call this method internally.
-  public Drawable getDrawableForDensity(int id, int density, Resources.Theme theme)
+  @NonNull
+  public Drawable getDrawableForDensity(int id, int density, @NonNull Resources.Theme theme)
       throws Exception {
     if (id == SPLASH_DRAWABLE_ID) {
       return new ColorDrawable(Color.BLUE);
diff --git a/shell/platform/android/test/io/flutter/plugins/GeneratedPluginRegistrant.java b/shell/platform/android/test/io/flutter/plugins/GeneratedPluginRegistrant.java
index c2528725b89b3..387de14de371f 100644
--- a/shell/platform/android/test/io/flutter/plugins/GeneratedPluginRegistrant.java
+++ b/shell/platform/android/test/io/flutter/plugins/GeneratedPluginRegistrant.java
@@ -1,5 +1,7 @@
 package io.flutter.plugins;
 
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
 import io.flutter.embedding.engine.FlutterEngine;
 import java.util.ArrayList;
@@ -13,7 +15,7 @@
 @VisibleForTesting
 public class GeneratedPluginRegistrant {
   private static final List<FlutterEngine> registeredEngines = new ArrayList<>();
-  public static RuntimeException pluginRegistrationException;
+  public static @Nullable RuntimeException pluginRegistrationException;
 
   /**
    * The one and only method currently generated by the tool.
@@ -21,7 +23,7 @@ public class GeneratedPluginRegistrant {
    * <p>Normally it registers all plugins in an app with the given {@code engine}. This fake tracks
    * all registered engines instead.
    */
-  public static void registerWith(FlutterEngine engine) {
+  public static void registerWith(@NonNull FlutterEngine engine) {
     if (pluginRegistrationException != null) {
       throw pluginRegistrationException;
     }
@@ -46,6 +48,7 @@ public static void clearRegisteredEngines() {
    * <p>CAUTION: This list is static and must be manually wiped in between test runs. See {@link
    * #clearRegisteredEngines()}.
    */
+  @NonNull
   public static List<FlutterEngine> getRegisteredEngines() {
     return new ArrayList<>(registeredEngines);
   }
diff --git a/tools/android_lint/bin/main.dart b/tools/android_lint/bin/main.dart
index a7a4dd77e82b0..99b750276fece 100644
--- a/tools/android_lint/bin/main.dart
+++ b/tools/android_lint/bin/main.dart
@@ -80,6 +80,9 @@ Future<int> runLint(ArgParser argParser, ArgResults argResults) async {
     if (!entity.path.endsWith('.java')) {
       continue;
     }
+    if (entity.path.endsWith('Test.java')) {
+      continue;
+    }
     projectXml.writeln('    <src file="${entity.path}" />');
   }
 
diff --git a/tools/android_lint/project.xml b/tools/android_lint/project.xml
index 75b87536362aa..ec80db6767fa6 100644
--- a/tools/android_lint/project.xml
+++ b/tools/android_lint/project.xml
@@ -5,10 +5,6 @@
   <module name="FlutterEngine" android="true" library="true" compile-sdk-version="android-S">
   <manifest file="../../../flutter/shell/platform/android/AndroidManifest.xml" />
     <src file="../../../flutter/shell/platform/android/test/io/flutter/TestUtils.java" />
-    <src file="../../../flutter/shell/platform/android/test/io/flutter/SmokeTest.java" />
-    <src file="../../../flutter/shell/platform/android/test/io/flutter/util/PathUtilsTest.java" />
-    <src file="../../../flutter/shell/platform/android/test/io/flutter/util/ViewUtilsTest.java" />
-    <src file="../../../flutter/shell/platform/android/test/io/flutter/util/PreconditionsTest.java" />
     <src file="../../../flutter/shell/platform/android/test/io/flutter/util/FakeKeyEvent.java" />
     <src file="../../../flutter/shell/platform/android/test/io/flutter/plugins/GeneratedPluginRegistrant.java" />
     <src file="../../../flutter/shell/platform/android/test/io/flutter/embedding/android/FlutterActivityTest.java" />