code: public org.tensorflow.framework.GraphDef getGraphDef() {
      return graphDef_ == null ? org.tensorflow.framework.GraphDef.getDefaultInstance() : graphDef_;
    }
docs: <pre>
  "graph_def" has the subgraph of nodes for this worker, with each node
  having its device_name filled in.
  </pre>
  
  <code>optional .tensorflow.GraphDef graph_def = 2;</code>