code: func (bsh *BufferedServerHeader) Add(key string, value string) {
  	if bsh.released {
  		bsh.original.Set(key, value)
  	} else {
  		old := []string{}
  		if v, found := bsh.headerMap[key]; found {
  			old = v
  		}
  		bsh.headerMap[key] = append(old, value)
  	}
  }
docs: // Add (append) to a key this value