code: def test_null_graph(self):
      G = nx.null_graph()
      assert g6.to_graph6_bytes(G) == b">>graph6<<?\n"
  
imports: from io import BytesIO
  import pytest
  import networkx
  import networkx.readwrite.graph6
  from networkx.utils import edges_equal, nodes_equal
label_desc: Use image node_id 1 for calling the TestToGraph6Bytes obj's underlying member method code with example usage: obj.test_null_graph() without return types