Calculated members in cross tab

Hi all,

I have a profit and losses in a cross tab created by a group and I need to add some rows to have the totals.

For example

Revenue 1

Revenue 2

Revenue 3

Total Revenue

Cost 1

Cost 2

Total Costs

....

For total revenue I used a calculated members with that formula:

GridValueAt(GetRowPathIndexOf("Revenue 1"), CurrentColumnIndex, CurrentSummaryIndex)

+ GridValueAt(GetRowPathIndexOf("Revenue 2"), CurrentColumnIndex, CurrentSummaryIndex)

+ GridValueAt(GetRowPathIndexOf("Revenue 3"), CurrentColumnIndex, CurrentSummaryIndex)

but the problem is that if I haven't for example any data for revenue 2 an error occurs -->argument # 1of "gridvalueat" is out of range.

It's possible to check if the argument exist??

thanks