code: func (s *Server) ListenAndServe() error {
  	if s.Server == nil {
  		return errors.New("use of http3.Server without http.Server")
  	}
  	return s.serveImpl(s.TLSConfig, nil)
  }
docs: // ListenAndServe listens on the UDP address s.Addr and calls s.Handler to handle HTTP/3 requests on incoming connections.