protected override ISingleStream <TOut> CreateOutputStream(EnsureSingleArgs <TOut> args)
 {
     return(base.CreateSingleStream(args.Input.Observable.Map((i, idx) =>
     {
         if (idx > 0)
         {
             throw new Exception($"{this.NodeName}: There are more than one element in the stream");
         }
         else
         {
             return i;
         }
     })));
 }
 public EnsureSingleStreamNode(string name, EnsureSingleArgs <TOut> args) : base(name, args)
 {
 }