def GetFileSystem(self, path_spec):
    """Retrieves a file system object defined by path specification.

    Args:
      path_spec (PathSpec): path specification.

    Returns:
      FileSystem: a file system object or None if not cached.
    """
    identifier = self._GetFileSystemCacheIdentifier(path_spec)
    return self._file_system_cache.GetObject(identifier)
Retrieves a file system object defined by path specification.

    Args:
      path_spec (PathSpec): path specification.

    Returns:
      FileSystem: a file system object or None if not cached.