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

  store_index = getattr(path_spec, 'store_index', None)

  if store_index is None:
    location = getattr(path_spec, 'location', None)

    if location is None or not location.startswith('/vss'):
      return None

    store_index = None
    try:
      store_index = int(location[4:], 10) - 1
    except (TypeError, ValueError):
      pass

    if store_index is None or store_index < 0:
      return None

  return store_index