code: def save_json(self, fpath):
      fp = open(fpath, "wt")
      strjs = json.dumps(self.get_json_trees())
      fp.write(strjs)
      fp.close()
  
imports: from __future__ import print_function
  from __future__ import division
  from __future__ import absolute_import
  import turicreate
  import unittest
  import json
  import random
  import numpy
  import pytest
label_desc: Use image node_id 9 for calling the GBDTDecoder obj's underlying member method code with example usage: obj.save_json(fpath) without return types