ViewData is null in view but not in controller

Question

I'm filling my ViewData in my controller and want to use the items inside the ViewData in my view. But the list which is filled using ViewData is always null.

Controller:

public ActionResult OrderReport()
{
    FillBagelCart();

    return this.ViewPdf("Order report", "ReportView");  
}

FillBagelCart is a function which fills ViewData["BagelCartItems"] = LstItems; I Debugged that and it's not empty.

View:

@{
 List<Tuple<BestelBagels.Models.Bagel, BestelBagels.Models.BagelType, int>> BagelCartItems = ViewData["BagelCartItems"] as List<Tuple<BestelBagels.Models.Bagel, BestelBagels.Models.BagelType, int>>;
}

When I am using this list, it is always null. So I have no idea what should be the reason?