[Android] error: cannot access ViewTreeObserver

[zp1ke]

I'm getting this error running the app on Android:

...\android\app\src\main\java\io\flutter\plugins\GeneratedPluginRegistrant.java:44: error: cannot access ViewTreeObserver
flutterEngine.getPlugins().add(new com.jrai.flutter_keyboard_visibility.FlutterKeyboardVisibilityPlugin());
^
class file for android.view.ViewTreeObserver not found

the app runs ok when removing the plugin,