code: def test_null_graph(self):
      g = Graph()
      plot(
          g,
          backend="cairo",
          target=result_image_folder / "graph_null.png",
      )
  
imports: import random
  import unittest
  from igraph import Graph, plot, VertexClustering
label_desc: Use image node_id 8 for calling the GraphTestRunner obj's underlying member method code with example usage: obj.test_null_graph() without return types