How do I use the strongly-typed HTML helpers with nullable types?

I want to use the strongly-typed HTML helpers in ASP.NET MVC 2 with a property of my model which is `Nullable<T>`. Model ``` public class TicketFilter { public bool? IsOpen { get; set; } public TicketType? Type{ get; set; } // TicketType is an enum // ... etc ... } ``` View (HTML) ``` <p>Ticket status: <%: Html.RadioButtonFor(m => m.IsOpen, null) %> All <%: Html.RadioButtonFor(m => m.IsOpen, true) %> Open <%: Html.RadioButtonFor(m => m.IsOpen, false) %> Closed </p> <p>Ticket type: <%: Html.RadioButtonFor(m => m.Type, null) %> Any <%: Html.RadioButtonFor(m => m.Type, TicketType.Question) %> Question <%: Html.RadioButtonFor(m => m.Type, TicketType.Complaint) %> Complaint <!-- etc --> </p> ``` However, using the helpers in this way throws an `ArgumentNullException` -- the second parameter cannot be null. Instead of `null`, I've tried using `new bool?()`/`new TicketType?` as well as `String.empty`. All result in the same exception. How can I work around this and bind a control to a null value?