code: def MetaGraph(self):
      
      if self._meta_graph is None:
        raise ValueError('There is no metagraph in this EventAccumulator')
      meta_graph = meta_graph_pb2.MetaGraphDef()
      meta_graph.ParseFromString(self._meta_graph)
      return meta_graph
docs: Return the metagraph definition, if there is one.
  
      Raises:
        ValueError: If there is no metagraph for this run.
  
      Returns:
        The `meta_graph_def` proto.