code: func (s *Scratch) SetX(k string, v interface{}) string {
  	s.init()
  
  	s.Lock()
  	defer s.Unlock()
  	if _, ok := s.values[k]; !ok {
  		s.values[k] = v
  	}
  	return ""
  }
docs: // SetX behaves the same as Set, except it will not overwrite existing keys if
  // already present.