docs: def enquire_graph(self, graph=None):
          """
          Verifies and returns relevant TensorFlow graph. If non-None graph were passed,
          the same graph is returned. Otherwise, nodes's graph is exposed and it is
          undefined the default TensorFlow graph is used.
  
          :param graph: TensorFlow graph or None. Default is None.
          :return: TensorFlow graph.
          """
          if graph is None:
              graph = self.root.graph if self.graph is None else self.graph
              if graph is None:
                  graph = tf.get_default_graph()
          return graph