bindings: Add empty checks for toV8()

Source/bindings/core/v8/V8MutationCallback.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 55 matching lines @@
     if (observerHandle.IsEmpty()) {
         if (!isScriptControllerTerminating())
             CRASH();
         return;
     }
 
     if (!observerHandle->IsObject())
         return;
 
     v8::Local<v8::Object> thisObject = v8::Local<v8::Object>::Cast(observerHandle);
-    v8::Local<v8::Value> argv[] = { toV8(mutations, m_scriptState->context()->Global(), isolate), observerHandle };
+    v8::Local<v8::Value> v8Mutations = toV8(mutations, m_scriptState->context()->Global(), isolate);
+    if (v8Mutations.IsEmpty())
+        return;
+    v8::Local<v8::Value> argv[] = { v8Mutations, observerHandle };
 
     v8::TryCatch exceptionCatcher;
     exceptionCatcher.SetVerbose(true);
     ScriptController::callFunction(executionContext(), m_callback.newLocal(isolate), thisObject, WTF_ARRAY_LENGTH(argv), argv, isolate);
 }
 
 void V8MutationCallback::setWeakCallback(const v8::WeakCallbackInfo<V8MutationCallback>& data)
 {
     data.GetParameter()->m_callback.clear();
 }
 
 DEFINE_TRACE(V8MutationCallback)
 {
     MutationCallback::trace(visitor);
     ActiveDOMCallback::trace(visitor);
 }
 
 } // namespace blink