public bool Poll(out IGroupedFlowable <K, V> item)
 {
     if (queue.Poll(out GroupedFlowable g))
     {
         item = g;
         return(true);
     }
     item = default(IGroupedFlowable <K, V>);
     return(false);
 }
 public bool Offer(IGroupedFlowable <K, V> item)
 {
     throw new InvalidOperationException("Should not be called!");
 }