Linq到XElement准备有一些条件

Question

private XElement GetClinicalClientPrice(int invid)
{
    using (MyDatabase db = new MyDatabase())
    {
        return new XElement("CLINICALCLIENTPRICE",
                       from ccp in db.TblClinicalClientPrice
                       where ccp.INVENTORY_ID == invid
                       select new XElement("Record",
                        new XElement("ITEM_ID",ccp.ITEM_ID),
                        new XElement("INVENTORY_ID", ccp.INVENTORY_ID),
                        new XElement("ITEM_DESCRIPTION", ccp.ITEM_DESCRIPTION),
                        new XElement("SUPPLIER_CAT", ccp.SUPPLIER_CAT),
                        new XElement("NDC_CODE", ccp.NDC_CODE),
                        new XElement("ITEM_NUMBER", ccp.ITEM_NUMBER),
                        new XElement("UOM", ccp.UOM),
                        new XElement("CONVERSION_FACTOR", ccp.CONVERSION_FACTOR),
                        new XElement("MANUFACTURER", ccp.MANUFACTURER),
                        new XElement("SESSION_ID", ccp.SESSION_ID),
                        new XElement("USERNAME", ccp.USERNAME),
                        new XElement("ENTRY_TIME", ccp.ENTRY_TIME),
                        new XElement("COST", ccp.COST),
                        new XElement("CLIENT_INPUT_ID", ccp.CLIENT_INPUT_ID),
                        new XElement("MHS_ITEM_ID", ccp.MHS_ITEM_ID),
                        new XElement("GUID", ccp.GUID),
                        new XElement("UNIQUE_ID", ccp.UNIQUE_ID),
                        new XElement("SUPPLIER_CAT_MODIFIED", ccp.SUPPLIER_CAT_MODIFIED),
                        new XElement("SIZE", ccp.SIZE),
                        new XElement("STRENGTH", ccp.STRENGTH)
                       ));
    }
}

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当我将上面生成的XElement插入数据库时​​，我得到（DateTime）空值异常。 我的例子是：stackoverflow.com/a/21163312/3121707