code: func UnwrapMemcachedError(rv *gomemcached.MCResponse,
  	err error) (*gomemcached.MCResponse, error) {
  
  	if rv == err {
  		return rv, nil
  	}
  	return rv, err
  }
docs: // UnwrapMemcachedError converts memcached errors to normal responses.
  //
  // If the error is a memcached response, declare the error to be nil
  // so a client can handle the status without worrying about whether it
  // indicates success or failure.