Linq-to-SQL using int? with a null value

I'm having some problems with a Linq-to-SQL query

Now if I run this request, everything run just fine and I get the right results back (2 rows).

return _repository.GetMenus()
                .Where(x => x.ParentId == null && x.WikiId == 1)
                .ToList();

But if I do the following, I just get an empty list.

var menu = new WikiMenu();
menu.ParentId = null;
return  _repository.GetMenus()
                   .Where(x => x.ParentId == menu.ParentId && x.WikiId == 1)
                   .ToList();

But if menu.ParentId is anything else then null it does work just fine.

This is the model WikiMenu

public class WikiMenu
{
    public int? Id { get; set; }
    public int WikiId { get; set; }
    public int PageId { get; set; }
    public string Title { get; set; }
    public int Order { get; set; }
    public int? ParentId { get; set; }
    public List<WikiMenu> SubMenu { get; set; }
}

How can I fix this?

So far have I done this little hack

if(menu.ParentId == null)
     return _repository.GetMenus()
                       .Where(x => x.ParentId == null && x.WikiId == site.Id)
                      开发者_如何学JAVA .ToList();
else
     return _repository.GetMenus()
                       .Where(x => x.ParentId == menu.ParentId && x.WikiId == site.Id)
                       .ToList();

You can try to use the following code:

return _repository.GetMenus().  
    Where(x => object.Equals(x.ParentId, menu.ParentId) && x.WikiId == 1).ToList();

This code snippet will force Linq2SQL to generate something like WHERE [table0].[parentId] IS NULL rather than WHERE [table0].[parentId] == NULL.

Hope this helps.