code: public org.tensorflow.framework.VersionDef getVersions() {
      return versions_ == null ? org.tensorflow.framework.VersionDef.getDefaultInstance() : versions_;
    }
docs: <pre>
  Compatibility versions of the graph.  See core/public/version.h for version
  history.  The GraphDef version is distinct from the TensorFlow version, and
  each release of TensorFlow will support a range of GraphDef versions.
  </pre>
  
  <code>optional .tensorflow.VersionDef versions = 4;</code>