docs: def new_node(self):
          """Adds a new, blank node to the graph.
          Returns the node id of the new node."""
          node_id = self.generate_node_id()
  
          node = {'id': node_id,
                  'edges': [],
                  'data': {}
          }
  
          self.nodes[node_id] = node
  
          self._num_nodes += 1
  
          return node_id