diff --git a/java/Android.mk b/java/Android.mk
index b580624..9b8b2b4 100644
--- a/java/Android.mk
+++ b/java/Android.mk
@@ -25,7 +25,7 @@
 
 LOCAL_JNI_SHARED_LIBRARIES := libjni_latinime
 
-LOCAL_STATIC_JAVA_LIBRARIES := android-common inputmethod-common android-support-v4
+LOCAL_STATIC_JAVA_LIBRARIES := android-common inputmethod-common android-support-v4 jsr305
 
 # Do not compress dictionary files to mmap dict data runtime
 LOCAL_AAPT_FLAGS := -0 .dict
diff --git a/java/src/com/android/inputmethod/event/Combiner.java b/java/src/com/android/inputmethod/event/Combiner.java
index 8b808c6..fee93f0 100644
--- a/java/src/com/android/inputmethod/event/Combiner.java
+++ b/java/src/com/android/inputmethod/event/Combiner.java
@@ -18,6 +18,8 @@
 
 import java.util.ArrayList;
 
+import javax.annotation.Nonnull;
+
 /**
  * A generic interface for combiners. Combiners are objects that transform chains of input events
  * into committable strings and manage feedback to show to the user on the combining state.
@@ -33,6 +35,7 @@
      * @param event the event to combine with the existing state.
      * @return the resulting event.
      */
+    @Nonnull
     Event processEvent(ArrayList<Event> previousEvents, Event event);
 
     /**
diff --git a/java/src/com/android/inputmethod/event/CombinerChain.java b/java/src/com/android/inputmethod/event/CombinerChain.java
index 8ddc9e7..f69bf4f 100644
--- a/java/src/com/android/inputmethod/event/CombinerChain.java
+++ b/java/src/com/android/inputmethod/event/CombinerChain.java
@@ -24,6 +24,8 @@
 import java.util.ArrayList;
 import java.util.HashMap;
 
+import javax.annotation.Nonnull;
+
 /**
  * This class implements the logic chain between receiving events and generating code points.
  *
@@ -87,6 +89,7 @@
      * @return the processed event. It may be the same event, or a consumed event, or a completely
      *   new event. However it may never be null.
      */
+    @Nonnull
     public Event processEvent(final ArrayList<Event> previousEvents, final Event newEvent) {
         final ArrayList<Event> modifiablePreviousEvents = new ArrayList<>(previousEvents);
         Event event = newEvent;
@@ -94,10 +97,6 @@
             // A combiner can never return more than one event; it can return several
             // code points, but they should be encapsulated within one event.
             event = combiner.processEvent(modifiablePreviousEvents, event);
-            if (null == event) {
-                // Combiners return null if they eat the event.
-                break;
-            }
         }
         return event;
     }
diff --git a/java/src/com/android/inputmethod/event/DeadKeyCombiner.java b/java/src/com/android/inputmethod/event/DeadKeyCombiner.java
index 342f499..d816247 100644
--- a/java/src/com/android/inputmethod/event/DeadKeyCombiner.java
+++ b/java/src/com/android/inputmethod/event/DeadKeyCombiner.java
@@ -23,6 +23,8 @@
 
 import java.util.ArrayList;
 
+import javax.annotation.Nonnull;
+
 /**
  * A combiner that handles dead keys.
  */
@@ -31,6 +33,7 @@
     final StringBuilder mDeadSequence = new StringBuilder();
 
     @Override
+    @Nonnull
     public Event processEvent(final ArrayList<Event> previousEvents, final Event event) {
         if (TextUtils.isEmpty(mDeadSequence)) {
             if (event.isDead()) {
diff --git a/java/src/com/android/inputmethod/event/MyanmarReordering.java b/java/src/com/android/inputmethod/event/MyanmarReordering.java
index 80c711f..7285512 100644
--- a/java/src/com/android/inputmethod/event/MyanmarReordering.java
+++ b/java/src/com/android/inputmethod/event/MyanmarReordering.java
@@ -21,6 +21,8 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 
+import javax.annotation.Nonnull;
+
 /**
  * A combiner that reorders input for Myanmar.
  */
@@ -128,6 +130,7 @@
                 : Event.createSoftwareTextEvent(combinedText, Event.NOT_A_KEY_CODE);
     }
 
+    @Nonnull
     @Override
     public Event processEvent(ArrayList<Event> previousEvents, Event newEvent) {
         final int codePoint = newEvent.mCodePoint;
diff --git a/java/src/com/android/inputmethod/latin/WordComposer.java b/java/src/com/android/inputmethod/latin/WordComposer.java
index 171d0bb..75d616e 100644
--- a/java/src/com/android/inputmethod/latin/WordComposer.java
+++ b/java/src/com/android/inputmethod/latin/WordComposer.java
@@ -25,6 +25,8 @@
 import java.util.ArrayList;
 import java.util.Collections;
 
+import javax.annotation.Nonnull;
+
 /**
  * A place to store the currently composing word with information such as adjacent key codes as well
  */
@@ -179,6 +181,7 @@
      * @param event the unprocessed event.
      * @return the processed event. Never null, but may be marked as consumed.
      */
+    @Nonnull
     public Event processEvent(final Event event) {
         final Event processedEvent = mCombinerChain.processEvent(mEvents, event);
         mEvents.add(event);