title: How to get Html.RenderAction to use my parameters?
body: <p>I have this in my RouteConfig.cs:</p>
  
  <pre><code>routes.MapRoute(
      name: "Promo",
      url: "Promo/{slug}",
      defaults: new { controller = "Promo", action = "Index", slug = UrlParameter.Optional }
  );
  </code></pre>
  
  <p>In PromoController.cs:</p>
  
  <pre><code>[ActionName("Index")]
  public ActionResult Index( string slug = "" )
  {
      // code that uses slug
  }
  </code></pre>
  
  <p>Then in a cshtml page I'm trying to do:</p>
  
  <pre><code>@{Html.RenderAction("Index", "Promo", "drink");}
  </code></pre>
  
  <p>But the "drink" parameter is not getting passed to my controller.</p>