ASP.NET MVC null model passed to controller action

Question

Why is a null parameter being passed to the following controller action?

 public FileContentResult GetImageForArticle(ArticleSummary article) 
        {             
            if (article == null || !article.ContainsValidThumbNail()) return null;            
            return File(article.ThumbNail, article.ThumbNaiType);
        }  

from the following partial view:

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<IEnumerable<AkwiMemorial.Models.ArticleSummary>>" %>
<%if (Model.Count() > 0)
  { %>
<table>    
    <% foreach (var item in Model)
       { %>    
        <tr>                        
             <td>  
               <img src='<%=Url.Action("GetImageForArticle", "Resources", new { article = item })%>' alt=""/>                                
            </td>
        </tr>

    <% } %>

    </table>

Answer 1

You cannot send complex objects like this:

<%=Url.Action("GetImageForArticle", "Resources", new { article = item })%>

Only simple scalar properties:

<%=Url.Action("GetImageForArticle", "Resources", new { 
    Id = item.Id,
    Foo = item.StringFoo,
    Bar = item.IntegerBar
})%>

So a good practice in this case is to only send an id:

<%=Url.Action("GetImageForArticle", "Resources", new { id = item.Id }) %>

and then have your controller action fetch the corresponding model from wherever it is stored give this id:

public ActionResult GetImageForArticle(int id) 
{             
    ArticleSummary article = _someRepository.GetArticle(id);
    if (article == null || !article.ContainsValidThumbNail()) 
    {
        return null;            
    }
    return File(article.ThumbNail, article.ThumbNaiType);
}