<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def GetVShadowStoreByPathSpec(self, path_spec):
 """Retrieves a VSS store for a path specification. Args: path_spec (PathSpec):
 path specification. Returns: pyvshadow.store: a VSS store or None if not available. """

    store_index = vshadow.VShadowPathSpecGetStoreIndex(path_spec)
    if store_index is None:
      return None

    return self._vshadow_volume.get_store(store_index)