code: func mergeValues(u1, u2 url.Values) url.Values {
  	if u1 == nil {
  		return u2
  	}
  	if u2 == nil {
  		return u1
  	}
  	for k, v := range u2 {
  		u1[k] = append(u1[k], v...)
  	}
  	return u1
  }
docs: // mergeValues returns the result of merging two url.Values.