static void _AddMiddleware(IApplicationBuilder app, IHostingEnvironment hostingEnvironment)
        {
            if (app == null)
            {
                throw new ArgumentNullException(nameof(app));
            }

            // ... need to add a static file provider for the default embedded content files for the controls ...

            app.AddCoreXTJS(hostingEnvironment);

            app.UseStaticFiles(new StaticFileOptions(new SharedOptions
            {
                FileProvider = new OverridableEmbeddedFileProvider(typeof(CoreXTToolkitForMvcApplicationBuilderExtensions).GetTypeInfo().Assembly, hostingEnvironment)
            }));
        }