protected Task ProcessItemAddMessage(ItemMessage <TIn> itemMessage)
        {
            var result = itemMessage.Items.SelectMany(_function).ToList();

            if (result.Count > 0)
            {
                StreamSender.EnqueueMessage(new ItemMessage <TOut>(result));
            }
            return(TaskDone.Done);
        }
        protected Task ProcessItemAddMessage(ItemMessage <TIn> itemMessage)
        {
            var resultList = itemMessage.Items.Where(item => _function(item)).ToList();

            if (resultList.Count > 0)
            {
                StreamSender.EnqueueMessage(new ItemMessage <TIn>(resultList));
            }

            return(TaskDone.Done);
        }