title: Url.routeUrl returns null (I've tried same questions)
body: <p>Hi everyone I wanna get url like {Controller}/{action}/{postid}-{address}
  but routUrl returns null please help me to solve it.(I'm newbie in MVC)</p>
  
  <p>my route config is</p>
  
  <pre><code>routes.MapRoute(
              name: "Post",
              url: "Posts/Show/{postid}-{address}",
              defaults: new { controller = "Posts", action = "Index", postid = "", address = "" }
             );
  </code></pre>
  
  <p>and index.cshtml</p>
  
  <pre><code>&lt;a href="@Url.RouteUrl("Post",new {item.PostId,item.Address })"&gt;@item.PostTitle&lt;/a&gt;
  </code></pre>
  
  <p>the url that generate is
  <a href="http://localhost:59066/Posts/Show/1-Post-with-Featured-Image" rel="nofollow">http://localhost:59066/Posts/Show/1-Post-with-Featured-Image</a></p>
  
  <p>but in PostsController </p>
  
  <pre><code>public ActionResult Show(string add)
      { return View();} 
  </code></pre>
  
  <p>"string add" is null !</p>