def get_passthrough_keys(cls) -> Iterable[str]:
    """Retrieves a user set passthrough_keys, None if not set."""
    state = cls._get_topmost_state_frame()
    if state.passthrough_keys is not None:
      return state.passthrough_keys
    return set()
Retrieves a user set passthrough_keys, None if not set.
tensorflow_transform/beam/context.py