I agree with Akuli that raising a KeyError is not expected behaviour (combined with the fact this is caught elsewhere), and therefore is probably a regression.

While we could use `winfo class` to determine the type of Tk widget, this would probably require a reasonably sized refactor of tkinter (and we would still need to support cases when it's a type we don't know). Therefore, I think returning `None` is the best solution.

Akuli, would you like to create a pull request for this?