@staticmethod
def tree_transitions_from_active_to_unsure_and_best_upstream_neighbor_is_null(
    interface: 'TreeInterfaceDownstream'):
    """
        Tree transitions from Active to Unsure state AND
        BestUpstream neighbor is null
        """
    interface.logger.debug(
        'tree_transitions_from_active_to_unsure_and_best_upstream_neighbor_is_null'
        )
    interface.send_i_am_no_longer_upstream()
