The type annotations on update_internal_user_password in lib/moodlelib.php do not allow for "null" to be passed in as password. This is appropriate in the case where the auth plugin never gets to handle the user's password - e.g. auth_oidc, which is broken by the addition of these type annotations.

It appears that the behaviour where null is passed in is otherwise acceptable, although a lot of the logic could probably be short-circuited in this case.