def func(
    endpoint: 'Endpoint',
    controller: 'Controller[BaseSerializer]',
) -> str | None:
    """Return ``request.user.pk`` when user should be throttled."""
    user = controller.request.user
    user_pk = getattr(user, 'pk', None)
    if (  # TODO: this is a bug in `WPS` :(
        user_pk is None  # noqa: WPS222
        or (getattr(user, 'is_superuser', False) and self.exclude_superuser)
        or (getattr(user, 'is_staff', False) and self.exclude_stuff)
    ):
        return None
    return str(user_pk)