title: jQuery $.ajax success not firing from JsonResult
body: <p>My code makes an ajax call:</p>
  
  <pre><code>$.ajax({
      url: "/Controller/EmailUserKeys",
      dataType: 'json',
      success: function () {
          alert('success');
      },
      error: function () {
          alert('error');
      }
  });
  </code></pre>
  
  <p>It calls an action in my controller which returns some JSON:</p>
  
  <pre><code>public JsonResult EmailUserKeys(string UserId)
  {
      ...
      return Json(new { success = true });
  }
  </code></pre>
  
  <p>My problem is that the ajax error function is called and not the ajax success function.</p>
  
  <p>Why?</p>
  
  <p>PS. If my action returns "return null;", the ajax success function is called.</p>