code: func (uuid UUID) String() string {
  	if len(uuid) != 16 {
  		return ""
  	}
  	var buf [36]byte
  	encodeHex(buf[:], uuid)
  	return string(buf[:])
  }
docs: // String returns the string form of uuid, xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
  // , or "" if uuid is invalid.