code: def test_null_graph(self):
      with pytest.raises(nx.NetworkXPointlessConcept):
          nx.average_shortest_path_length(nx.null_graph())
  
imports: import pytest
  import networkx
label_desc: Use image node_id 8 for calling the TestAverageShortestPathLength obj's underlying member method code with example usage: obj.test_null_graph() without return types