code: func IsNotFoundError(err error) bool {
  	es := err.Error()
  	for _, str := range iptablesNotFoundStrings {
  		if strings.Contains(es, str) {
  			return true
  		}
  	}
  	return false
  }
docs: // IsNotFoundError returns true if the error indicates "not found".  It parses
  // the error string looking for known values, which is imperfect; beware using
  // this function for anything beyond deciding between logging or ignoring an
  // error.