def stream_results_optional(
    f: Callable[..., Optional[PagedResult[TResult, TToken]]], *args, **kwargs
) -> Optional[Iterable[TResult]]:
    """Like stream_results(), but for functions ``f`` that return an Optional.

    """
    if "page_token" in kwargs:
        raise TypeError('stream_results has no argument "page_token".')
    res = f(*args, page_token=None, **kwargs)
    if res is None:
        return None
    else:
        return stream_results(f, *args, **kwargs)