问不存在汇总节点时LINQ to XML异常

EN

SyndicationFeed combinedfeed = new SyndicationFeed(newFeed1.Items.Union(newFeed2.Items).OrderByDescending(u => u.PublishDate));

//save the filtered xml file to a folder
XDocument filteredxmlfile = new XDocument(
             new XDeclaration("2.0", "utf-8", "yes"),
             new XElement("channel",
             from filteredlist in combinedfeed.Items
             select new XElement("item",
                  new XElement("title", filteredlist.Title.Text),
                  new XElement("source", FormatContent(filteredlist.Links[0].Uri.ToString())[0]),
                  new XElement("url", FormatContent(filteredlist.Links[0].Uri.ToString())[1]),
                  new XElement("pubdate", filteredlist.PublishDate.ToString("r")),
                  new XElement("date",filteredlist.PublishDate.Date.ToShortDateString()),
// I get an exception here as the summary/ description node is not present for all the items in the syndication feed
new XElement("date",filteredlist.Summary.Text)
                  )));
string savexmlpath = Server.MapPath(ConfigurationManager.AppSettings["FilteredFolder"]) + "sorted.xml";
filteredxmlfile.Save(savexmlpath);