dispose method
@mustCallSuper, override
Discards any resources used by the object. After this is called, the object is not in a usable state and should be discarded (calls to addListener and removeListener will throw after the object is disposed).
This method should only be called by the object's owner.
Implementation
@override
@mustCallSuper
Future<void> dispose() async {
super.dispose();
return Future.value();
}