docs: def Flush(self):
      """Flush the data to the index."""
      super(LabelSet, self).Flush()
  
      self.to_delete = self.to_delete.difference(self.to_set)
  
      with data_store.DB.GetMutationPool() as mutation_pool:
        mutation_pool.LabelUpdateLabels(
            self.urn, self.to_set, to_delete=self.to_delete)
      self.to_set = set()
      self.to_delete = set()