Crash when using with Android embedding V2

[schricb]

We have upgraded our app to support Android Embedding V2. The app attempts to launch and then immediately crashes:

2021-05-07 14:53:51.474 9171-9171/org.my.app E/MethodChannel#: Parameter messenger must not be null.
2021-05-07 14:53:51.474 9171-9171/org.my.app D/AndroidRuntime: Shutting down VM
2021-05-07 14:53:51.480 9171-9171/org.my.app E/AndroidRuntime: FATAL EXCEPTION: main
Process: org.my.app, PID: 9171
java.lang.NullPointerException: Attempt to invoke interface method 'void io.flutter.plugin.common.BinaryMessenger.setMessageHandler(java.lang.String, io.flutter.plugin.common.BinaryMessenger$BinaryMessageHandler)' on a null object reference
at io.flutter.plugin.common.MethodChannel.setMethodCallHandler(MethodChannel.java:119)
at com.pichillilorenzo.flutter_appavailability.AppAvailability.registerWith(AppAvailability.java:37)
at io.flutter.plugins.GeneratedPluginRegistrant.registerWith(GeneratedPluginRegistrant.java:24)
at org.my.app.MainActivity.configureFlutterEngine(MainActivity.kt:54)
at io.flutter.embedding.android.FlutterFragment.configureFlutterEngine(FlutterFragment.java:1016)
at io.flutter.embedding.android.FlutterActivityAndFragmentDelegate.onAttach(FlutterActivityAndFragmentDelegate.java:180)
at io.flutter.embedding.android.FlutterFragment.onAttach(FlutterFragment.java:608)
at androidx.fragment.app.Fragment.performAttach(Fragment.java:2672)
at androidx.fragment.app.FragmentStateManager.attach(FragmentStateManager.java:253)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1168)
at androidx.fragment.app.FragmentTransition.addToFirstInLastOut(FragmentTransition.java:1255)
at androidx.fragment.app.FragmentTransition.calculateFragments(FragmentTransition.java:1138)
at androidx.fragment.app.FragmentTransition.startTransitions(FragmentTransition.java:136)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1987)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1945)
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1847)
at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:2621)
at androidx.fragment.app.FragmentManager.dispatchActivityCreated(FragmentManager.java:2569)
at androidx.fragment.app.FragmentController.dispatchActivityCreated(FragmentController.java:247)
at androidx.fragment.app.FragmentActivity.onStart(FragmentActivity.java:541)
at org.my.app.MainActivity.onStart(MainActivity.kt:178)
at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1413)
at android.app.Activity.performStart(Activity.java:7169)
at android.app.ActivityThread.handleStartActivity(ActivityThread.java:3155)
at android.app.servertransaction.TransactionExecutor.performLifecycleSequence(TransactionExecutor.java:180)
at android.app.servertransaction.TransactionExecutor.cycleToPath(TransactionExecutor.java:165)
at android.app.servertransaction.TransactionExecutor.executeLifecycleState(TransactionExecutor.java:142)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:70)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1986)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:215)
at android.app.ActivityThread.main(ActivityThread.java:6939)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:870)

[schricb]

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 2.0.6, on macOS 11.3.1 20E241 darwin-x64, locale en-US)
[!] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
✗ Android license status unknown.
Run flutter doctor --android-licenses to accept the SDK licenses.
See https://flutter.dev/docs/get-started/install/macos#android-setup for more details.
[✓] Xcode - develop for iOS and macOS
[✓] Chrome - develop for the web
[✓] Android Studio (version 4.2)
[✓] VS Code (version 1.56.0)
[✓] Connected device (3 available)

! Doctor found issues in 1 category.