MVC Model is null in OnExecuted action filter … or a more elegant way to set the model?

I have an ActionFilter with an override on the OnActionExecuted method. The filterContext.Controller.ViewData.Model is always null on a POST operation. I did find the following article that seems to be saying that it should not be null but this must have been an earlier version of MVC. This is MVC3. What should I be getting?

Model availability inside ActionFilter

UPDATE:

I've figured out the answer to the original question. I had a custom ActionResult that outputs JSON with a custom date formatter. The problem was that the model is not being set in the controller.

In my custom ActionResult the ExecuteResult method get passed the ControllerContext which would be nice if I could set the Model there:

context.Controller.ViewData.Model = _data;

But this is to late in the cycle and the result is still null in the ActionFilter. This seems to mean that I need to manually set the model in the controller:

ControllerContext.Controller.ViewData.Model = model; 

Or

View(model);

Which then means I need to remember to do this every time I use this custom ActionResult. Is there a more elegant way?

YET ANOTHER UPDATE:

I found a way to do this it just isn't as elegant as I hoped.

In my constructor for the comstom ActionResult I sending in the controller, that way at least it will alway be consistent:

public JsonNetResult(object data, Controller controller) {
    SerializerSettings = new JsonSerializerSettings();
    _data = data;
    controller.ControllerContext.Controller.ViewData.Model = _data;
}