code: func (u UUID) String() string {
  	if u == nil || len(u) != 16 {
  		return "00000000-0000-0000-0000-000000000000"
  	}
  	b := []byte(u)
  	return fmt.Sprintf("%08x-%04x-%04x-%04x-%012x", b[:4], b[4:6], b[6:8], b[8:10], b[10:])
  }
docs: //
  // String produces the standard "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx" representaion of a UUID.
  //