[pp-2] Clean up method default to use NULL for Hook Attributes

FWIW, Hook is a class that exists in 11.1, there are likely no subclasses yet, but changing the type like that is a technically a BC break. So will need a decision on whether that's important enough to warrant that or this is a won't fix.

Thanks for opening this issue based on my feedback at #3489141.

Sad panda. I wish we were consistent with this sort of thing. It's too bad we released Hook with this slightly weird DX. It's definitely minor, no real harm done the way it is, other than the mild WTF.

If this is "[PP-2]", it should be postponed, and the summary should say what it's blocked on.

Thanks,
-Derek