code: def test_null_graph(self):
      G = nx.DiGraph()
      assert list(nx.weakly_connected_components(G)) == []
      assert nx.number_weakly_connected_components(G) == 0
      with pytest.raises(nx.NetworkXPointlessConcept):
          next(nx.is_weakly_connected(G))
  
file_path: networkx/networkx/algorithms/components/tests/test_weakly_connected.py
imports: import pytest
  import networkx
  from networkx import NetworkXNotImplemented
label_desc: Use image node_id 5 for calling the TestWeaklyConnected obj's underlying member method code with example usage: obj.test_null_graph() without return types