code: def get_used_fields(payload):
      
      return [
          tag
          for tag, descriptor in payload.CHILD_MAP.items()
          if descriptor.__get__(payload, type(payload)) is not None
      ]
docs: Get a list containing the names of the fields that are used in the
      xso.Query.
  
      :param payload: Query object o be
      :type payload: :class:`~aioxmpp.ibr.Query`
      :return: :attr:`list`