code: def first_key(self):
      if len(self) == 0:
          raise ValueError("IntMap is empty.")
      return self.added_keys[0]
  
imports: from enum import IntEnum
  from typing import List
  import numpy
  from onnx.reference.op_run import OpRun
label_desc: Use image node_id 4 for calling the IntMap obj's underlying member method code with example usage: obj.first_key() and returns: self