当DateTime为null的时候 如何转换我？

C# code

                var query = from order in orders.AsEnumerable()                            orderby order.Field<int>("Status") ascending, order.Field<DateTime>("CreateOn") descending                            select new                            {                                OrderID = order.Field<int>("OrderID"),                                ProductName = order.Field<string>("ProductName"),                                Price = order.Field<decimal>("Price"),                                Count = order.Field<int>("Count"),                                Status = order.Field<int>("Status"),                                PayMoney = order.Field<decimal>("PayMoney"),                                PayDate = order.Field<DateTime>("PayDate"),                                CheckName = order.Field<string>("CheckName"),                                Tel = order.Field<string>("Tel"),                                CheckAddress = order.Field<string>("CheckAddress"),                                Freight = order.Field<int>("Freight")                            };

PayDate = order.Field<DateTime>("PayDate"),就是这句
当字段"PayDate"为的时候，程序会出错

请问如何转换？
不是说Field<T>()可以支持null的吗？

[解决办法]
order.Field<DateTime?>

可空结构才允许null值...