I'm trying to create an optional parameter.  It is a dollar range that the user can enter with a value for low and a value for high.  I want the user to be able to enter values if they want, otherwise don't enter anything.  It seems no matter what options I try, something must be entered in this range.  I've tried setting the edit mask using all 9, all 0, or all a.  It still forced me to enter something.