code: func appendValuesURL(u *url.URL, values ...url.Values) *url.URL {
  	merged := u.Query()
  
  	for _, v := range values {
  		for k, vv := range v {
  			merged[k] = append(merged[k], vv...)
  		}
  	}
  
  	u.RawQuery = merged.Encode()
  	return u
  }
docs: // appendValuesURL appends the parameters to the url.