code: def serialize(self):
      visited = set()
      next_id = [0]
  
      def _id():
          next_id[0] += 1
          return next_id[0]
  
      def create_node(node):
          constant = None
          op = None
  
          if isinstance(node, namespace.DecisionOperator):
              if node in visited:
                  return node.name
              else:
                  node.name = "{}_{}".format(node.op_name, _id())
                  visited.add(node)
              input_dep_map = {}
              for name, arg in node.arguments().items():
                  if arg is not None:
                      input_dep_map[name] = create_node(arg)
              op = config.Operator(
                  name=node.name,
                  op_name=node.op_name,
                  input_dep_map=input_dep_map,
              )
          else:
              constant = config.Constant(
                  name="constant_{}".format(_id()), value=node
              )
  
          if constant is not None:
              self.constants.append(constant)
              return constant.name
          elif op is not None:
              self.operators.append(op)
              return op.name
          else:
              raise TypeError("Invalid type: {}".format(node))
  
      if self.root_op is None:
          raise ValueError("Need to set root operator before exporting")
  
      if not isinstance(self.root_op, namespace.DecisionOperator):
          raise ValueError("The root node has to be an operator")
  
      create_node(self.root_op)
  
file_path: ReAgent/serving/reagent/serving/config/builder.py
imports: from typing import Any, Dict
  import reagent.serving.config.config
  import reagent.serving.config.namespace
  import reagent.serving.config.operators
  from reagent.serving.config.serialize import config_to_json
label_desc: Use image node_id 6 for calling the DecisionPlanBuilder obj's underlying member method code with example usage: obj.serialize() and returns: next_id, constant, node, op