[Flutter] Flutter: FCM Unhandled Exception: Null check operator used on a null value

E/flutter (26872): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: Null check operator used on a null value E/flutter (26872): #0
MethodChannelFirebaseMessaging.registerBackgroundMessageHandler (package:firebase_messaging_platform_interface/src/method_channel/method_channel_messaging.dart:173:53) E/flutter (26872): #1
FirebaseMessagingPlatform.onBackgroundMessage= (package:firebase_messaging_platform_interface/src/platform_interface/platform_interface_messaging.dart:108:16)
​

// Background Messaging Set Up
Future<void> _firebaseMessagingBackgroundHandler(
RemoteMessage message) async {
print('background message');
}

FirebaseMessaging.onBackgroundMessage(_firebaseMessagingBackgroundHandler);
runApp(....)


I am getting an error for this code on Android system. Everything works except when the app is terminated.

What works on Android:

• Notification when Terminated, onBackground and onForeground
• Date only when onForeground

What does not work on Android:

• Data only when Terminated and onBackground

What works on iOS:

• Notification when Terminated, onBackground and onForeground
• Date only when onForeground

What does not work on iOS:

• Data only when Terminated,

I have no clue why I am getting that null value error on Android system and how can I fix this issue? Also, is it true that I can not receive the Data only push notification on iOS when the app is terminated?

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