No matching calls. All calls: method(Instance of Object)

I am trying to verify if my method is called with the arguments I am interested in. However, it seems to be working only with primitive types. Instead of returning my object, it just says Instance of MyAnswer. Why does this happen?

test('Compute answers', () async {
    when(myService.submitAnswer(any, any)).thenAnswer((_) async {});
    final model = MyModel();
    model.submit(); // This calls myService.submitAnswer(MyAnswer(...), 123)).
    verify(myService.submitAnswer(MyAnswer(...), 123).called(1);
  });

This throws No matching calls. All calls: MyService.submitAnswer(Instance of 'MyAnswer', 123).