OIptionalFieldDAO.cs

    public class OptionalFieldDAO
    {
        private int? maybeValue_;

        public OptionalFieldDAO(int? maybeValue)
        {
            maybeValue_ = maybeValue;
        }

        public bool Value(out int value)
        {
            if(maybeValue_.HasValue)
            {
                value = maybeValue_.Value;
                return true;
            }
            value = 0;
            return false;
        }

        public static void Main(string[] args)
        {
            OptionalFieldDAO realValue = new OptionalFieldDAO(1);
            OptionalFieldDAO noValue = new OptionalFieldDAO(null);
        }
    }