code: def force_valid_bson_key(key):
      key = str(key)
      if key.startswith("$"):
          key = "@" + key[1:]
      key = key.replace(".", ",")
      return key
  
imports: from typing import Optional, Union
  import mimetypes
  import os.path
  import pickle
  import re
  import sys
  import time
  from tempfile import NamedTemporaryFile
  import warnings
  import sacred.optional
  from sacred.commandline_options import cli_option
  from sacred.dependencies import get_digest
  from sacred.observers.base import RunObserver
  from sacred.observers.queue import QueueObserver
  from sacred.serializer import flatten
  from sacred.utils import ObserverError, PathType
  import pkg_resources
label_desc: Use image node_id 1 for calling a global function with example usage: force_valid_bson_key(key) and returns: key