class_docstr: A cache of ForwardMsgs.
  
  Large ForwardMsgs (e.g. those containing big DataFrame payloads) are
  stored in this cache. The server can choose to send a ForwardMsg's hash,
  rather than the message itself, to a client. Clients can then
  request messages from this cache via another endpoint.
  
  This cache is *not* thread safe. It's intended to only be accessed by
  the server thread.
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docstr: Return the message with the given ID if it exists in the cache.
  
  Parameters
  ----------
  hash : str
      The id of the message to retrieve.
  
  Returns
  -------
  ForwardMsg | None
docstr_tok: ["Return","the","message","with","the","given","ID","if","it","exists","in","the","cache",".","Parameters","--","--","--","--","--","hash",":","str","The","id","of","the","message","to","retrieve",".","Returns","--","--","--","-","ForwardMsg","|","None"]
code: def get_message(self, hash: str) -> Optional[ForwardMsg]:
      """Return the message with the given ID if it exists in the cache.
  
      Parameters
      ----------
      hash : str
          The id of the message to retrieve.
  
      Returns
      -------
      ForwardMsg | None
  
      """
      entry = self._entries.get(hash, None)
      return entry.msg if entry else None
  
imports: import hashlib
  from typing import TYPE_CHECKING, Dict, List, MutableMapping, Optional
  from weakref import WeakKeyDictionary
  from streamlit import config, util
  from streamlit.logger import get_logger
  from streamlit.proto.ForwardMsg_pb2 import ForwardMsg
  from streamlit.runtime.stats import CacheStat, CacheStatsProvider, group_stats
  from streamlit.util import HASHLIB_KWARGS
label_desc: Use image node_id 4 for calling the ForwardMsgCache obj's underlying member method code with example usage: obj.get_message(hash) and returns: unknown