code: func GetInnerNonRetryableError(err error) error {
  	for err != nil {
  		if _, ok := err.(nonRetryableError); ok {
  			return InnerError(err)
  		}
  		err = InnerError(err)
  	}
  	return nil
  }
docs: // GetInnerNonRetryableError returns an inner non-retryable error
  // if contained by this error, nil otherwise.