code: func IsNotFoundError(err error) bool {
  	es := err.Error()
  	if strings.Contains(es, "does not exist") {
  		// set with the same name already exists
  		// xref: https://github.com/Olipro/ipset/blob/master/lib/errcode.c#L32-L33
  		return true
  	}
  	if strings.Contains(es, "element is missing") {
  		// entry is missing from the set
  		// xref: https://github.com/Olipro/ipset/blob/master/lib/parse.c#L1904
  		// https://github.com/Olipro/ipset/blob/master/lib/parse.c#L1925
  		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 but works in
  // practice.