Display None if field is empty

I am grouping my report on a field called Crew. This field is sometimes empty and so the group header doesn't show anything. I want that if this field is empty the report should display 'none' instead of just leaving it blank. How can I do that?
ThanksUse a formula to display the group header. Ie, if Crew is Group #1 :

If IsNull(Group#1Name) then
"None"
else
Group#1Name

Group Header names are available through formula editor the same as all other report/database fields.|||Thanks for replying kristyw. I am new to Crystal. Where should I put this formula?|||Create a new formula and drag it onto your form.|||It gives me an error saying "The ) is missing" and highlisghts Group on the first line.

If IsNull(Group#6Name) then
"None"
else
Group#6Name|||Here's my working formula :

If IsNull(GroupName ({VRP_CUST_DETAILS.ACCOUNTNUMBER})) then
"None"
else
GroupName ({VRP_CUST_DETAILS.ACCOUNTNUMBER})

Learn how to use CR Formula Editor - it's very handy when it comes to creating these types of formulas as you can drag the field names into it and easily find all the available functions.|||Thanks, that works just fine.