public Task Handle(InventoryNotificationReceived notification, CancellationToken cancellationToken)
 {
     HandledInventoryNotificationReceived++;
     return(Task.FromResult(0));  // This is called twice.
 }
 public Task <EmptyResponse> Handle(InventoryNotificationReceived notification, CancellationToken cancellationToken)
 {
     HandledInventoryNotificationReceived++;
     return(EmptyResponse.Task); // This is called twice.
 }