/// <summary>
/// Returns a future to the last value from a sequence, or the default for that type
/// if no value is produced.
/// </summary>
/// <param name="source">The source data-producer.</param>
public static IFuture <TSource> LastOrDefault <TSource>(this IDataProducer <TSource> source)
{
return(source.LastOrDefault(x => true));
}