title: Request.UrlReferrer.ToString() ->System.NullReferenceException: Object reference not set to an instance of an object
body: <p>When I try <code>Request.UrlReferrer.ToString()</code> this error occures:</p>
  
  <blockquote>
    <p>System.NullReferenceException: Object reference not set to an instance of an object</p>
  </blockquote>