Answer
Instead of trying to pass a literal static value, control whether the parameter is populated at all, per menu item: for the menu item that should show the Summary, map the Quick Report parameter's Source Key Name to a real field that's always populated on the record (like Line No) — guaranteeing the parameter always has a value; for the menu item that should suppress the Summary, simply don't map that Quick Report parameter at all, leaving it null. Inside the Crystal report itself, use an ISNULL() check against that parameter to decide whether to show or suppress the Summary section — this achieves the same per-menu-item fixed behavior that trying to pass a literal static value directly couldn't.