module.exports should default to an empty object.

sky/engine/core/app/Module.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef SKY_ENGINE_CORE_APP_MODULE_H_
 #define SKY_ENGINE_CORE_APP_MODULE_H_
 
 #include "sky/engine/core/app/AbstractModule.h"
 
 namespace blink {
 class Application;
 
 class Module : public AbstractModule {
   DEFINE_WRAPPERTYPEINFO();
 public:
   static PassRefPtr<Module> create(ExecutionContext* context,
                                    Application* application,
                                    PassRefPtr<Document> document,
                                    const String& url) {
     return adoptRef(new Module(context, application, document, url));
   }
 
   virtual ~Module();
 
   Application* application() const { return application_.get(); }
 
-  void setExports(const ScriptValue& exports) { exports_ = exports; }
-  const ScriptValue& exports() const { return exports_; }
+  void setExports(ScriptState*, const ScriptValue& exports);
+  const ScriptValue& exports(ScriptState*) const;
 
 private:
   Module(ExecutionContext* context,
          Application* application,
          PassRefPtr<Document> document,
          const String& url);
   const AtomicString& interfaceName() const override;
 
   Application* GetApplication() override;
 
   RefPtr<Application> application_;
-  ScriptValue exports_;
+  mutable ScriptValue exports_;
 };
 
 } // namespace blink
 
 #endif  // SKY_ENGINE_CORE_APP_MODULE_H_