code: def find_substring_edge(self, substring, suffix_tree_id):
          
          suffix_tree = self.suffix_tree_repo[suffix_tree_id]
          started = datetime.datetime.now()
          edge, ln = find_substring_edge(substring=substring, suffix_tree=suffix_tree, edge_repo=self.edge_repo)
          # if edge is not None:
          #     print("Got edge for substring '{}': {}".format(substring, edge))
          # else:
          #     print("No edge for substring '{}'".format(substring))
          print(" - searched for edge in {} for substring: '{}'".format(datetime.datetime.now() - started, substring))
          return edge, ln
docs: Returns an edge that matches the given substring.