Crystal Reports Printing Optional/Multiple Number Parameter

Message

     I'm using Crystal 2008 with Oracle DB

I have an optional number parm that can accept multiple entries.  I want to print this in the header or "All" if they didn't enter anything.

This formula works fine if something is entered in the parm but gives me an error when nothing is entered.  The error "Parameter has no value"

I've tried putting an if hasvalue check in front but it still does not like it.

Any help is appreciated.

My ultimate goal is to either print the word "All" or the actual parm values. 

numbervar counter; 
stringvar display; 
for counter := 1 to count({?Fare Instrument}) do ( 
display := display + totext({?Fare Instrument}[counter],0,"") + ", ");
left(display, len(display)-2);