如何从WUAPI的DownloadContents获取DownloadUrl

Question

我想获取Windows更新补丁的下载URL，我的代码是

        var session = new UpdateSession();
        var searcher = session.CreateUpdateSearcher();
        var searchType = "Type='Software' and IsInstalled =0";

        searcher.Online = false;
        var searchResult = searcher.Search(searchType);
        var collection = searchResult.Updates;

        foreach (IUpdate item in collection)
        {
            outpu("Title: \t{0}", item.Title);
            outpu("UpdateId: \t{0}", item.Identity.UpdateID);
            outpu("Description: \t{0}", item.Description);
            if (item.KBArticleIDs[0] == "2592687")
            {
                Trace.WriteLine("what");
            }
            if ((item.BundledUpdates.Count > 0) && (item.BundledUpdates[0].DownloadContents.Count >0))
                outpu("DownloadUrl: \t{0}", item.BundledUpdates[0].DownloadContents[0].DownloadUrl);
        }

通常我可以获得下载网址，但有时我不能。  例如，

时

KBArticleIDs = "2592687"

debug显示“DownloadContents”没有子节点，那我该怎么办？