title: Data from ajax post is passing null to the controller
body: <pre><code>AJAX call - 
  </code></pre>
  
  <p>Here countryId is passed as "AU" for example - </p>
  
  <pre><code>$("#Countries").change(function () {
          var countryId = this.value;
          $.ajax({
              url: '/Registers/GetStates',
              type: "POST",
              data: { 'data': countryId },
              success: function (states) {
                  $("#States").html(""); // clear before appending new list 
                  $.each(states, function (i, state) {
                      $("#States").append(
                          $('&lt;option&gt;&lt;/option&gt;').val(state.Id).html(state.Name));
                  });
              }
          });
      });
  </code></pre>
  
  <p>After calling the GetStates method 'countryId' is always passed as null in the controller method. Not sure what I'm missing here. 
  I tried JSON.Stringify({ 'data': countryId }) also. Can anyone help me out ?</p>
  
  <pre><code>Controller Action - 
  
  [HttpPost]
  public SelectList GetStates(string countryId)
  {
       return Helper.GetStates(countryId);
  }
  </code></pre>