Error create an Image widget in Kentico 12 MVC

I unable create an image widget with custom controller.

I copied all souce code used to build Image widget in Dancing Goat example. There is no error from my source code, but I got this error message after I click Image widget from Kentico CMS:

An error has occurred. If the problem persists, contact your system administrator.

I don't know where error accurred with my Image widget, no error happen if I click another widgets as: Text or Number widget.

After copied Image widget in Dancing Goat example, I just custom my controller as below:

using System;
using System.Linq;
using System.Web.Mvc;

using CMS.DocumentEngine;

using Kentico.PageBuilder.Web.Mvc;

using News.Controllers.Widgets;
using News.Models.Widgets;
using News.Models.Widgets.ImageWidget;

[assembly: RegisterWidget("News.Widgets.ImageWidget", typeof(ImageWidgetController), "Photo", Description = "Add a Photo", IconClass = "icon-picture")]

namespace News.Controllers.Widgets
{
    public class ImageWidgetController : WidgetController<ImageWidgetProperties>
    {

        /// <summary>
        /// Creates an instance of <see cref="ImageWidgetController"/> class.
        /// </summary>
        /// <param name="outputCacheDependencies">Output cache dependencies.</param>

        /// <summary>
        /// Creates an instance of <see cref="ImageWidgetController"/> class.
        /// </summary>
        /// <param name="propertiesRetriever">Retriever for widget properties.</param>
        /// <param name="currentPageRetriever">Retriever for current page where is the widget used.</param>
        /// <param name="outputCacheDependencies">Output cache dependencies.</param>
        /// <remarks>Use this constructor for tests to handle dependencies.</remarks>
        public ImageWidgetController(IComponentPropertiesRetriever<ImageWidgetProperties> propertiesRetriever, ICurrentPageRetriever currentPageRetriever) 
            : base(propertiesRetriever, currentPageRetriever)
        {
        }


        public ActionResult Index()
        {
            var properties = GetProperties();
            var image = GetImage(properties);

            return PartialView("Widgets/_ImageWidget", new ImageWidgetViewModel
            {
                Image = image
            });
        }


        private DocumentAttachment GetImage(ImageWidgetProperties properties)
        {
            var page = GetPage();
            return page?.AllAttachments.FirstOrDefault(x => x.AttachmentGUID == properties.ImageGuid);

        }
    } 
}

Basically, I only remove CacheDependencies.

Can someone help me?