[firebase_messaging] FirebaseMessaging.onBackgroundMessage causes the application crash

[abdullahrs]

Before Flutter 2 and null-security, my firebase services were working fine. I wanted to update it according to the documentation. I followed documentation instructions but I get this error and the app is closing immediately. I tried many things but did not get any results.
I just added these, am I doing something wrong?
main.dart file:

// imports ...

final FlutterLocalNotificationsPlugin flutterLocalNotificationsPlugin =
    FlutterLocalNotificationsPlugin();

const AndroidNotificationChannel channel = AndroidNotificationChannel(
  'high_importance_channel', // id
  'High Importance Notifications', // title
  'This channel is used for important notifications.', // description
  importance: Importance.high,
);

Future<void> _firebaseMessagingBackgroundHandler(RemoteMessage message) async {
  await Firebase.initializeApp();
  print('Handling a background message ${message.messageId}');
}

Future<void> main() async {
  WidgetsFlutterBinding.ensureInitialized();
  await UserPreferences().init();
  
  Initialize.instance.init();

  await Firebase.initializeApp();

  // ? Error occurs here
  // FirebaseMessaging.onBackgroundMessage(_firebaseMessagingBackgroundHandler);

  await flutterLocalNotificationsPlugin
      .resolvePlatformSpecificImplementation<
          AndroidFlutterLocalNotificationsPlugin>()
      ?.createNotificationChannel(channel);
      
  await FirebaseMessaging.instance.setForegroundNotificationPresentationOptions(
    alert: true,
    badge: true,
    sound: true,
  );
  //...
}

Error:

Launching lib\main.dart on sdk gphone x86 arm in debug mode...
lib\main.dart:1
√ Built build\app\outputs\flutter-apk\app-debug.apk.
I/Choreographer( 7761): Skipped 131 frames! The application may be doing too much work on its main thread.
Connecting to VM Service at ws://127.0.0.1:52375/z4dqvdo3Op4=/ws
I/FLTFireBGExecutor( 7761): Creating background FlutterEngine instance, with args: [--start-paused, --enable-dart-profiling]
D/EGL_emulation( 7761): eglCreateContext: 0xe9d52140: maj 3 min 0 rcv 3
D/EGL_emulation( 7761): eglCreateContext: 0xe9d50a80: maj 3 min 0 rcv 3
D/HostConnection( 7761): HostConnection::get() New Host Connection established 0xe9d52220, tid 7827
D/HostConnection( 7761): HostComposition ext ANDROID_EMU_CHECKSUM_HELPER_v1 ANDROID_EMU_native_sync_v2 ANDROID_EMU_native_sync_v3 ANDROID_EMU_native_sync_v4 ANDROID_EMU_dma_v1 ANDROID_EMU_direct_mem ANDROID_EMU_host_composition_v1 ANDROID_EMU_host_composition_v2 ANDROID_EMU_vulkan ANDROID_EMU_deferred_vulkan_commands ANDROID_EMU_vulkan_null_optional_strings ANDROID_EMU_vulkan_create_resources_with_requirements ANDROID_EMU_YUV_Cache ANDROID_EMU_async_unmap_buffer ANDROID_EMU_vulkan_ignored_handles ANDROID_EMU_vulkan_free_memory_sync ANDROID_EMU_vulkan_shader_float16_int8 ANDROID_EMU_vulkan_async_queue_submit GL_OES_EGL_image_external_essl3 GL_OES_vertex_array_object GL_KHR_texture_compression_astc_ldr ANDROID_EMU_host_side_tracing ANDROID_EMU_async_frame_commands ANDROID_EMU_gles_max_version_3_0
D/EGL_emulation( 7761): eglMakeCurrent: 0xe9d50a80: ver 3 0 (tinfo 0xab9518d0) (first time)
D/AndroidRuntime( 7761): Shutting down VM
E/AndroidRuntime( 7761): FATAL EXCEPTION: main
E/AndroidRuntime( 7761): Process: com.abta.mrc, PID: 7761
E/AndroidRuntime( 7761): java.lang.ClassCastException: io.flutter.embedding.engine.plugins.shim.ShimPluginRegistry cannot be cast to io.flutter.embedding.engine.FlutterEngine
E/AndroidRuntime( 7761): at com.abta.mrc.Application.registerWith(Application.java:25)
E/AndroidRuntime( 7761): at io.flutter.plugins.firebase.messaging.FlutterFirebaseMessagingBackgroundExecutor.lambda$null$0$FlutterFirebaseMessagingBackgroundExecutor(FlutterFirebaseMessagingBackgroundExecutor.java:206)
E/AndroidRuntime( 7761): at io.flutter.plugins.firebase.messaging.-$$Lambda$FlutterFirebaseMessagingBackgroundExecutor$Tw1_-iY8wcRJPWf1qeylRYPPEZI.run(Unknown Source:6)
E/AndroidRuntime( 7761): at android.os.Handler.handleCallback(Handler.java:938)
E/AndroidRuntime( 7761): at android.os.Handler.dispatchMessage(Handler.java:99)
E/AndroidRuntime( 7761): at android.os.Looper.loop(Looper.java:223)
E/AndroidRuntime( 7761): at android.app.ActivityThread.main(ActivityThread.java:7656)
E/AndroidRuntime( 7761): at java.lang.reflect.Method.invoke(Native Method)
E/AndroidRuntime( 7761): at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
E/AndroidRuntime( 7761): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
I/Process ( 7761): Sending signal. PID: 7761 SIG: 9
Lost connection to device.
Exited (sigterm)

flutter doctor -v

[√] Flutter (Channel stable, 2.0.4, on Microsoft Windows [Version 10.0.19042.867], locale tr-TR)
• Flutter version 2.0.4 at C:\src\flutter
• Framework revision b1395592de (9 days ago), 2021-04-01 14:25:01 -0700
• Engine revision 2dce47073a
• Dart version 2.12.2

[√] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
• Android SDK at C:\Users\Abdul\AppData\Local\Android\sdk
• Platform android-30, build-tools 30.0.3
• Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)
• All Android licenses accepted.

[√] Chrome - develop for the web
• Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe

[√] Android Studio (version 4.1.0)
• Android Studio at C:\Program Files\Android\Android Studio
• Flutter plugin can be installed from:
https://plugins.jetbrains.com/plugin/9212-flutter
• Dart plugin can be installed from:
https://plugins.jetbrains.com/plugin/6351-dart
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)

[√] VS Code (version 1.55.1)
• VS Code at C:\Users\Abdul\AppData\Local\Programs\Microsoft VS Code
• Flutter extension version 3.21.0

[√] Connected device (3 available)
• sdk gphone x86 arm (mobile) • emulator-5554 • android-x86 • Android 11 (API 30) (emulator)
• Chrome (web) • chrome • web-javascript • Google Chrome 89.0.4389.114
• Edge (web) • edge • web-javascript • Microsoft Edge 88.0.705.74

• No issues found!

[abdullahrs]

I only deleted "onBackgroundMessage" method. It looks like it is working without it.

[StatTark]

well done!