diff --git a/java/src/com/android/inputmethod/keyboard/TextDecorator.java b/java/src/com/android/inputmethod/keyboard/TextDecorator.java
index ddc65bf..2b7d2ce 100644
--- a/java/src/com/android/inputmethod/keyboard/TextDecorator.java
+++ b/java/src/com/android/inputmethod/keyboard/TextDecorator.java
@@ -303,7 +303,7 @@
      */
     private static final class LayoutInvalidator {
         private final HandlerImpl mHandler;
-        public LayoutInvalidator(final TextDecorator ownerInstance) {
+        public LayoutInvalidator(@Nonnull final TextDecorator ownerInstance) {
             mHandler = new HandlerImpl(ownerInstance);
         }
 
@@ -311,7 +311,7 @@
 
         private static final class HandlerImpl
                 extends LeakGuardHandlerWrapper<TextDecorator> {
-            public HandlerImpl(final TextDecorator ownerInstance) {
+            public HandlerImpl(@Nonnull final TextDecorator ownerInstance) {
                 super(ownerInstance);
             }
 
diff --git a/java/src/com/android/inputmethod/keyboard/internal/DrawingHandler.java b/java/src/com/android/inputmethod/keyboard/internal/DrawingHandler.java
index 4f8a105..1a55359 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/DrawingHandler.java
+++ b/java/src/com/android/inputmethod/keyboard/internal/DrawingHandler.java
@@ -23,6 +23,8 @@
 import com.android.inputmethod.latin.SuggestedWords;
 import com.android.inputmethod.latin.utils.LeakGuardHandlerWrapper;
 
+import javax.annotation.Nonnull;
+
 // TODO: Separate this class into KeyPreviewHandler and BatchInputPreviewHandler or so.
 public class DrawingHandler extends LeakGuardHandlerWrapper<Callbacks> {
     public interface Callbacks {
@@ -34,7 +36,7 @@
     private static final int MSG_DISMISS_KEY_PREVIEW = 0;
     private static final int MSG_DISMISS_GESTURE_FLOATING_PREVIEW_TEXT = 1;
 
-    public DrawingHandler(final Callbacks ownerInstance) {
+    public DrawingHandler(@Nonnull final Callbacks ownerInstance) {
         super(ownerInstance);
     }
 
diff --git a/java/src/com/android/inputmethod/keyboard/internal/TimerHandler.java b/java/src/com/android/inputmethod/keyboard/internal/TimerHandler.java
index ec7b9b0..80b299b 100644
--- a/java/src/com/android/inputmethod/keyboard/internal/TimerHandler.java
+++ b/java/src/com/android/inputmethod/keyboard/internal/TimerHandler.java
@@ -27,6 +27,8 @@
 import com.android.inputmethod.latin.Constants;
 import com.android.inputmethod.latin.utils.LeakGuardHandlerWrapper;
 
+import javax.annotation.Nonnull;
+
 // TODO: Separate this class into KeyTimerHandler and BatchInputTimerHandler or so.
 public final class TimerHandler extends LeakGuardHandlerWrapper<Callbacks> implements TimerProxy {
     public interface Callbacks {
@@ -45,7 +47,7 @@
     private final int mIgnoreAltCodeKeyTimeout;
     private final int mGestureRecognitionUpdateTime;
 
-    public TimerHandler(final Callbacks ownerInstance, final int ignoreAltCodeKeyTimeout,
+    public TimerHandler(@Nonnull final Callbacks ownerInstance, final int ignoreAltCodeKeyTimeout,
             final int gestureRecognitionUpdateTime) {
         super(ownerInstance);
         mIgnoreAltCodeKeyTimeout = ignoreAltCodeKeyTimeout;
diff --git a/java/src/com/android/inputmethod/latin/LatinIME.java b/java/src/com/android/inputmethod/latin/LatinIME.java
index 77016cb..b989cf2 100644
--- a/java/src/com/android/inputmethod/latin/LatinIME.java
+++ b/java/src/com/android/inputmethod/latin/LatinIME.java
@@ -110,6 +110,8 @@
 import java.util.Locale;
 import java.util.concurrent.TimeUnit;
 
+import javax.annotation.Nonnull;
+
 /**
  * Input method implementation for Qwerty'ish keyboard.
  */
@@ -208,7 +210,7 @@
         private int mDelayInMillisecondsToUpdateSuggestions;
         private int mDelayInMillisecondsToUpdateShiftState;
 
-        public UIHandler(final LatinIME ownerInstance) {
+        public UIHandler(@Nonnull final LatinIME ownerInstance) {
             super(ownerInstance);
         }
 
diff --git a/java/src/com/android/inputmethod/latin/setup/SetupWizardActivity.java b/java/src/com/android/inputmethod/latin/setup/SetupWizardActivity.java
index 54562f3..c3b30dc 100644
--- a/java/src/com/android/inputmethod/latin/setup/SetupWizardActivity.java
+++ b/java/src/com/android/inputmethod/latin/setup/SetupWizardActivity.java
@@ -42,6 +42,8 @@
 
 import java.util.ArrayList;
 
+import javax.annotation.Nonnull;
+
 // TODO: Use Fragment to implement welcome screen and setup steps.
 public final class SetupWizardActivity extends Activity implements View.OnClickListener {
     static final String TAG = SetupWizardActivity.class.getSimpleName();
@@ -82,7 +84,7 @@
 
         private final InputMethodManager mImmInHandler;
 
-        public SettingsPoolingHandler(final SetupWizardActivity ownerInstance,
+        public SettingsPoolingHandler(@Nonnull final SetupWizardActivity ownerInstance,
                 final InputMethodManager imm) {
             super(ownerInstance);
             mImmInHandler = imm;
diff --git a/java/src/com/android/inputmethod/latin/utils/LeakGuardHandlerWrapper.java b/java/src/com/android/inputmethod/latin/utils/LeakGuardHandlerWrapper.java
index dd6fac6..9a5be99 100644
--- a/java/src/com/android/inputmethod/latin/utils/LeakGuardHandlerWrapper.java
+++ b/java/src/com/android/inputmethod/latin/utils/LeakGuardHandlerWrapper.java
@@ -21,21 +21,22 @@
 
 import java.lang.ref.WeakReference;
 
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+
 public class LeakGuardHandlerWrapper<T> extends Handler {
     private final WeakReference<T> mOwnerInstanceRef;
 
-    public LeakGuardHandlerWrapper(final T ownerInstance) {
+    public LeakGuardHandlerWrapper(@Nonnull final T ownerInstance) {
         this(ownerInstance, Looper.myLooper());
     }
 
-    public LeakGuardHandlerWrapper(final T ownerInstance, final Looper looper) {
+    public LeakGuardHandlerWrapper(@Nonnull final T ownerInstance, final Looper looper) {
         super(looper);
-        if (ownerInstance == null) {
-            throw new NullPointerException("ownerInstance is null");
-        }
         mOwnerInstanceRef = new WeakReference<>(ownerInstance);
     }
 
+    @Nullable
     public T getOwnerInstance() {
         return mOwnerInstanceRef.get();
     }