getting notif.action=null while using FCM.getInitialNotification()

Before openning an issue
1. Reproduce it with the example project in this repo.
2. If you can't receive iOS notification, make sure you can receive notification using quickstart-ios project provided by Firebase team

When openning an issue, please include following information for better support

1. What version of RN and react-native-fcm are you running?
2. What device are you using? (e.g iOS9 emulator, Android 6 device)?
3. Is your app running in foreground, background or not running?

Start by reproducing the issue with the repository's example project and inspect FCM.getInitialNotification() where notif.action is reported as null. If iOS notifications cannot be received, compare behavior with Firebase's quickstart-ios project; the issue needs concrete reproduction details and a confirmed cause before a fix can be defined.

Written by the indexing model from the issue text.