AppStateManager provides the method public void attachAll(Iterable<AppState> states).
Unfortunately this does not support subclasses of Appstate. I suggest adapt this method signature to: public void attachAll(Iterable<? extends AppState> states).
PS: I m not very familiar with open source contribution. Is it possible for me create a pull request and wait for approval?
I do have trouble coming up with a good use-case for it, though. In the interest of maybe helping you out of a different design issue, what are you trying to do that requires this?