code: func strDurationAddDuration(sc *stmtctx.StatementContext, d string, arg1 types.Duration) (string, error) {
  	arg0, err := types.ParseDuration(sc, d, types.MaxFsp)
  	if err != nil {
  		return "", err
  	}
  	tmpDuration, err := arg0.Add(arg1)
  	if err != nil {
  		return "", err
  	}
  	tmpDuration.Fsp = types.MaxFsp
  	if tmpDuration.MicroSecond() == 0 {
  		tmpDuration.Fsp = types.MinFsp
  	}
  	return tmpDuration.String(), nil
  }
docs: // strDurationAddDuration adds duration to duration string, returns a string value.