title: HttpPostedFile in File Upload process is NULL if I use AJAX
body: <p>I am using file upload functionality in my asp.net MVC project.
  It worked great until I started using some AJAX functionality on my page.</p>
  
  <p>The HttpPostedFile is always NULL on Ajax page.</p>
  
  <p>How can solve this issue along with calling ajax on my page?</p>