Диалог загрузки файла Sitecore, возвращающий ноль Args.Result в PostBack (Sitecore 8.2, C #)

Question

У меня есть пользовательская кнопка ленты Sitecore для импорта данных из загруженного файла.Диалог импорта работает, но когда он переходит в обратную передачу, args.HasResult возвращается как false

public abstract class ImportCommand : Command
{
    protected const string XamlControlPage = "/sitecore/shell/~/xaml/Sitecore.Shell.Applications.Dialogs.Bayer.UploadFile.aspx";
    private const string MasterDb = "master";

    protected ISitecoreService SitecoreService;
    protected IItemService ItemService;

    /// <summary>
    /// Executes the command in the specified context.
    /// </summary>
    /// <param name="context">The context.</param>
    public override void Execute(CommandContext context)
    {
        Initialize();

        Assert.ArgumentNotNull(context, "context");
        if (context.Items.Length != 1)
            return;

        Item obj = context.Items[0];
        var parameters = new NameValueCollection();
        parameters["uri"] = obj.Uri.ToString();
        parameters["id"] = obj.ID.ToString();
        Context.ClientPage.Start(this, "RunPipeline", parameters);
    }

    protected void Initialize()
    {
        var db = Sitecore.Configuration.Factory.GetDatabase("master");
        SitecoreService = new SitecoreService(db);
        ItemService = new ItemService(SitecoreService);
    }

    protected void RunPipeline(ClientPipelineArgs args)
    {
        if (!args.IsPostBack)
        {
            var url = new UrlString(UIUtil.GetUri(XamlControlPage));
            SheerResponse.ShowModalDialog(url.ToString(), "580", "300", string.Empty, true);
            args.WaitForPostBack(true);
            return;
        }

        if (!args.HasResult)
            return;

        try
        {
            var itemId = new Guid(args.Parameters["id"]);
            using (new BulkUpdateContext())
            {
                DoStuff(itemId, args.Result);
            }
            SheerResponse.Alert("Import Successful. Press OK to continue.");
        }
        catch (Exception ex)
        {
            SheerResponse.ShowError(ex);
        }
        finally
        {
            // Try deleting the file
            try
            {
                File.Delete(args.Result);
            }
            catch (Exception e)
            {
                Sitecore.Diagnostics.Log.Warn(string.Format("Unable to delete file: {0}", args.Result), e, this);
            }
        }
    }
}

У меня есть файл UploadFile.cs, который обрабатывает диалог:

public class UploadFile : DialogPage
{
    protected FileUpload fileUpload;
    protected Literal ltrlResult;

    protected bool IsFirstLoad
    {
        get { return ViewState["Upload.IsFirst"] as string != "false"; }
        set { ViewState["Upload.IsFirst"] = !value ? "false" : null; }
    }

    protected string FilePath
    {
        get { return ViewState["Upload.FilePath"] as string; }
        set { ViewState["Upload.FilePath"] = value; }
    }

    protected override void OnLoad(EventArgs e)
    {
        if (IsFirstLoad)
        {
            ltrlResult.Text = "First upload a file, then click OK.";
            IsFirstLoad = false;
        }
        else
        {
            ltrlResult.Text = string.Empty;

            var fileOK = false;
            var path = HttpContext.Current.Server.MapPath("~/Upload/");
            if (fileUpload.HasFile)
            {
                var fileExtension = Path.GetExtension(fileUpload.FileName).ToLower();
                string[] allowedExtensions = {".csv"};
                for (int i = 0; i < allowedExtensions.Length; i++)
                {
                    if (fileExtension == allowedExtensions[i])
                    {
                        fileOK = true;
                    }
                }
            }

            if (fileOK)
            {
                try
                {
                    var filePath = path + fileUpload.FileName;
                    fileUpload.PostedFile.SaveAs(filePath);

                    FilePath = filePath;

                    ltrlResult.Text = "File uploaded successfully. Press OK to continue.";
                }
                catch (Exception ex)
                {
                    ltrlResult.Text = "File could not be uploaded.";
                    Sitecore.Diagnostics.Log.Error("File could not be uploaded.", ex, typeof (UploadFile));
                }
            }
            else
            {
                ltrlResult.Text = "Cannot accept files of this type.";
            }
        }

        base.OnLoad(e);
    }

    protected override void OK_Click()
    {
        if (string.IsNullOrEmpty(FilePath))
        {
            SheerResponse.ShowError("You must first upload a file.", string.Empty);
            return;
        }

        SheerResponse.SetDialogValue(FilePath);

        SheerResponse.Alert(
                "The import process is starting. This may take a few minutes. \n\nPress OK to continue, and wait until the import confirmation popup appears.");


        base.OK_Click();
    }
}

Загрузка успешно завершена, она устанавливает SheerResponse.SetDialogValue(FilePath), но когда я возвращаюсь к обратной передаче ImportTrials, args.HasResult имеет значение false и args.Result имеет значение null