class_docstr: Unit tests for the :func:`networkx.algorithms.approximation.max_clique`
  function.
code: def test_null_graph(self):
      G = nx.null_graph()
      assert len(max_clique(G)) == 0
  
file_path: networkx/networkx/algorithms/approximation/tests/test_clique.py
imports: import networkx
  from networkx.algorithms.approximation import clique_removal, large_clique_size, max_clique, maximum_independent_set
label_desc: Use image node_id 1 for calling the TestMaxClique obj's underlying member method code with example usage: obj.test_null_graph() without return types