void IObserver <WorkDoneProgress> .OnError(Exception error) =>
 _router.SendNotification(
     WorkDoneToken.Create(_onError?.Invoke(error) ?? new WorkDoneProgressEnd {
     Message = error.ToString()
 }, _serializer.JsonSerializer)
     );
 public void OnNext(WorkDoneProgress value) => _router.SendNotification(
     WorkDoneToken.Create(value, _serializer.JsonSerializer)
     );
 public void OnCompleted() => _router.SendNotification(
     WorkDoneToken.Create(_onComplete?.Invoke() ?? new WorkDoneProgressEnd {
     Message = ""
 }, _serializer.JsonSerializer)
     );