code: def test_tree_all_pairs_lca_nonexisting_pairs_exception(self):
      lca = tree_all_pairs_lca(self.DG, 0, [(-1, -1)])
      pytest.raises(nx.NodeNotFound, list, lca)
      # check if node is None
      lca = tree_all_pairs_lca(self.DG, None, [(-1, -1)])
      pytest.raises(nx.NodeNotFound, list, lca)
  
imports: from itertools import chain, combinations, product
  import pytest
  import networkx
label_desc: Use image node_id 12 for calling the TestTreeLCA obj's underlying member method code with example usage: obj.test_tree_all_pairs_lca_nonexisting_pairs_exception() without return types