[firebase_messaging] Background messages not delivered in versions newer than 6.0.3

[LinusU]

Describe the bug
When upgrading from version 6.0.3 of firebase_messaging our onBackgroundMessage handler is no longer called. Instead the following error is printed to the Android log:

I/flutter (20210): Unable to handle incoming background message.
I/flutter (20210): NoSuchMethodError: The method 'call' was called on null.
I/flutter (20210): Receiver: null
I/flutter (20210): Tried calling: call(_LinkedHashMap len:1)

This occurs even if my handler is just a simple print statement, thus the null.call(...) doesn't happen in my handler.

Here is where the error is logged from:

https://github.com/FirebaseExtended/flutterfire/blob/547674c8b550a0b14ff442a3bd6a2663c6dc7680/packages/firebase_messaging/lib/firebase_messaging.dart#L37-L43

To Reproduce
Steps to reproduce the behavior:

1. Add firebase_messaging version 6.0.3
2. Add a background handler that prints something to the log
3. See that the message is received
4. Upgrade to the latest firebase_messaging version
5. See that the message is no longer received

Expected behavior
The message should be received with both versions.

Additional context
n/a

[iapicca]

Hi @LinusU
can you please provide your flutter doctor -v,
your pubspec.yaml
and your flutter run --verbose?
Thank you

[mklim]

From a discussion in our team chat: this is likely caused by a bug in how we added Android v2 embedding support. See also flutter/flutter#47406, which is showing similar symptoms when running in the background because of a change in the v2 embedding.

/cc @bparrishMines

[thesmalleyes]

Hi @mklim any update for this issue? cause i can't see notification in background untill now.
@LinusU do you have a solution? i need your help for this issue