module.exports should default to an empty object.

sky/engine/core/app/Module.h

Index: sky/engine/core/app/Module.h
diff --git a/sky/engine/core/app/Module.h b/sky/engine/core/app/Module.h
index 29ff7c5ef8b70bdc9fa514df65cfa5529b04a6a6..525b62734f9b2317118509768782d70c2685330e 100644
--- a/sky/engine/core/app/Module.h
+++ b/sky/engine/core/app/Module.h
@@ -24,8 +24,8 @@ public:
 
   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,
@@ -37,7 +37,7 @@ private:
   Application* GetApplication() override;
 
   RefPtr<Application> application_;
-  ScriptValue exports_;
+  mutable ScriptValue exports_;
 };
 
 } // namespace blink