<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _process_path_prefix(path_prefix):
 """Validate and process a Google Cloud Stoarge path prefix. Args: path_prefix: a Google Cloud Storage path prefix of format '/bucket/prefix' or '/bucket/' or '/bucket'. Raises: ValueError: if path is invalid. Returns: a tuple of /bucket and prefix. prefix can be None. """

  _validate_path(path_prefix)
  if not _GCS_PATH_PREFIX_REGEX.match(path_prefix):
    raise ValueError('Path prefix should have format /bucket, /bucket/, '
                     'or /bucket/prefix but got %s.' % path_prefix)
  bucket_name_end = path_prefix.find('/', 1)
  bucket = path_prefix
  prefix = None
  if bucket_name_end != -1:
    bucket = path_prefix[:bucket_name_end]
    prefix = path_prefix[bucket_name_end + 1:] or None
  return bucket, prefix