/// <inheritdoc />
 public override string ToString()
 {
     if (OptionalResultSelector != null)
     {
         return(string.Format(
                    "Aggregate({0}, {1}, {2})",
                    Seed.BuildString(),
                    Func.BuildString(),
                    OptionalResultSelector.BuildString()));
     }
     else
     {
         return(string.Format(
                    "Aggregate({0}, {1})",
                    Seed.BuildString(),
                    Func.BuildString()));
     }
 }