title: Upload is null after adding jquery.unobtrusive-ajax.js reference
body: <p>If I don't refer <code>jquery.unobtrusive-ajax.js</code> I can get attachment on Post. If I refer it It's giving me null.</p>
  
  <pre><code>&lt;script src="~/Scripts/jquery.unobtrusive-ajax.js"&gt;&lt;/script&gt;
  
  
  @using (Ajax.BeginForm("Index", "ContactSubmission", new AjaxOptions{ InsertionMode = InsertionMode.Replace, HttpMethod = "POST", OnSuccess = "updateSuccess" },
       new { enctype = "multipart/form-data",@class = "form-horizontal", role = "form" }))
        {
                 ///code here
  </code></pre>
  
  <p>}</p>
  
  <pre><code>[HttpPost]
  public JsonResult Index(Contact contact)
  {
      if (ModelState.IsValid)
      {
         if (contact != null)
         {
           string attachment = string.Empty;
           // HttpPostedFileBase Attachment
           if (contact.Attachment != null) attachment = SaveFile(contact.Attachment); 
                  ......
  </code></pre>
  
  <p>How to handle this?</p>