Ajax Upload helper in asp.net mvc 5 didn't work and gets Null value

I want to save image using Upload control in asp.net mvc 5 using Razor engine . These are my codes below , I think every thing is OK but I don't know why UploadImage in controller gets null and didn't get selected image . could any one help me please ?

admin controller

according to a article I used same name @html.upload("UploadImage") in controller parameters.

[HttpPost]
    public ActionResult AddSubGood(SubGood subgood, HttpPostedFileBase UploadImage)
    {
        var MainGoodId = subgood.FKMainGoodID;
        SubGoodRepositories blSubGood = new SubGoodRepositories();
        if (ModelState.IsValid)
        {
            subgood.FKMainGoodID = MainGoodId;
            if (blSubGood.Add(subgood))
            {
                return MessageBox.Show("added successfully", MessageType.Success);
            }
            else
            {
                return MessageBox.Show(" didn't add", MessageType.Error);
            }
        }
        else
        {
            return MessageBox.Show(ModelState.GetErrors(), MessageType.Warning);
        }

    }

AddSubGood.cshtml

according to a article, I added enctype="multipart/form-data" to form

@using (Ajax.BeginForm("Admin", "AddSubGood", new AjaxOptions { HttpMethod = "Post", Url = "/Admin/AddSubGood" }, new{enctype="multipart/form-data" }))
{
 @Html.AntiForgeryToken()
 <div class="form-group">
             <div class="form-group">
               <div class="col-md-10">
                   @Html.Upload("UploadImage")
                   @Html.ValidationMessageFor(model => model.SubGoodURL)
               </div>
            @Html.LabelFor(model => model.SubGoodURL, new { @class = "control-label col-md-2" })
   </div>
}

UploadHelper.cs

 public static class UploadHelper
  {
  public static MvcHtmlString Upload(this HtmlHelper helper, string name, object htmlAttributes = null)
  {
    TagBuilder input = new TagBuilder("input");
    input.Attributes.Add("type", "file");
    input.Attributes.Add("id", helper.ViewData.TemplateInfo.GetFullHtmlFieldId(name));
    input.Attributes.Add("name", helper.ViewData.TemplateInfo.GetFullHtmlFieldName(name));

    if (htmlAttributes != null)
    {
        var attributes = HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes);
        input.MergeAttributes(attributes);
    }

    return new MvcHtmlString(input.ToString());
}

public static MvcHtmlString UploadFor<TModel, TValue>(this HtmlHelper<TModel> helper, Expression<Func<TModel, TValue>> expression, object htmlAttributes = null)
{
    //helper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(ExpressionHelper.GetExpressionText(expression))
    var data = ModelMetadata.FromLambdaExpression(expression, helper.ViewData);
    TagBuilder input = new TagBuilder("input");
    input.Attributes.Add("type", "file");
    input.Attributes.Add("id", helper.ViewData.TemplateInfo.GetFullHtmlFieldId(ExpressionHelper.GetExpressionText(expression)));
    input.Attributes.Add("name", helper.ViewData.TemplateInfo.GetFullHtmlFieldName(ExpressionHelper.GetExpressionText(expression)));

    if (htmlAttributes != null)
    {
        var attributes = HtmlHelper.AnonymousObjectToHtmlAttributes(htmlAttributes);
        input.MergeAttributes(attributes);
    }

    return new MvcHtmlString(input.ToString());
   }
}