code: def last_refresh_time(self):
      try:
          return self._soft_lock_path.stat().st_mtime
      except FileNotFoundError:
          return None
  
imports: import os
  import logging
  import pathlib
  import threading
  import uuid
  import time
  from filelock import BaseFileLock, SoftFileLock, UnixFileLock, has_fcntl
  from cachetools.func import ttl_cache
  from psutil import disk_partitions
  from typing import Optional, Union, Dict, Set, Tuple
label_desc: Use image node_id 7 for calling the RefreshLock obj's underlying member method code with example usage: obj.last_refresh_time() and returns: self, None