bindings: Add empty checks for toV8()

Source/bindings/core/v8/custom/V8PopStateEventCustom.cpp

 /*
  * Copyright (C) 2010 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 65 matching lines @@
 
     // There's no cached value from a previous invocation, nor a state value was provided by the
     // event, but there is a history object, so first we need to see if the state object has been
     // deserialized through the history object already.
     // The current history state object might've changed in the meantime, so we need to take care
     // of using the correct one, and always share the same deserialization with history.state.
 
     bool isSameState = history->isSameAsCurrentState(event->serializedState());
 
     if (isSameState) {
-        v8::Local<v8::Object> v8History = toV8(history, info.Holder(), info.GetIsolate()).As<v8::Object>();
+        v8::Local<v8::Value> v8HistoryValue = toV8(history, info.Holder(), info.GetIsolate());
+        if (v8HistoryValue.IsEmpty())
+            return;
+        v8::Local<v8::Object> v8History = v8HistoryValue.As<v8::Object>();
         if (!history->stateChanged()) {
             result = V8HiddenValue::getHiddenValue(info.GetIsolate(), v8History, V8HiddenValue::state(info.GetIsolate()));
             if (!result.IsEmpty()) {
                 v8SetReturnValue(info, cacheState(info.Holder(), result, info.GetIsolate()));
                 return;
             }
         }
         result = event->serializedState()->deserialize(info.GetIsolate());
         V8HiddenValue::setHiddenValue(info.GetIsolate(), v8History, V8HiddenValue::state(info.GetIsolate()), result);
     } else {
         result = event->serializedState()->deserialize(info.GetIsolate());
     }
 
     v8SetReturnValue(info, cacheState(info.Holder(), result, info.GetIsolate()));
 }
 
 } // namespace blink