code: def test_null_graph(self):
      assert nx.number_of_nodes(nx.null_graph()) == 0
  
imports: import itertools
  import typing
  import pytest
  import networkx
  from networkx.algorithms.isomorphism.isomorph import graph_could_be_isomorphic
  from networkx.utils import edges_equal, nodes_equal
label_desc: Use image node_id 27 for calling the TestGeneratorClassic obj's underlying member method code with example usage: obj.test_null_graph() without return types