React Native出現"Native module cannot be null"問題

經查跟PushNotification有關，需要手動完成Linking。
兩步解決此問題：

• 配置Linking Libraries:https://facebook.github.io/react-native/docs/linking-libraries-ios.html#manual-linking
• 配置PushNotificationIOS:
  https://facebook.github.io/react-native/docs/pushnotificationios.html

參考

https://github.com/facebook/react-native/issues/5612