code: def save_json(self, obj, filename):
      with open(os.path.join(self.dir, filename), "w") as f:
          json.dump(flatten(obj), f, sort_keys=True, indent=2)
          f.flush()
  
imports: import json
  import os
  import os.path
  from pathlib import Path
  from typing import Optional
  import warnings
  from shutil import copyfile, SameFileError
  from sacred.commandline_options import cli_option
  from sacred.dependencies import get_digest
  from sacred.observers.base import RunObserver
  from sacred import optional
  from sacred.serializer import flatten
  from sacred.utils import PathType
label_desc: Use image node_id 12 for calling the FileStorageObserver obj's underlying member method code with example usage: obj.save_json(obj, filename) without return types