[REPORT] How to show blank fields instead of "NaN" values

Hi everyone,

I'm a student and I have a problem with my report. I'm trying to show salesperson's commission for every month based on Cust. Ledger Entry and Detailed Cust. Ledg. Entry. In situation, when for salesperson there are no entries, my report shows NaN value instead of blank. Do you know how to handle with this problem or how to change displaying for 0 value? It is specially annoying in Date's field.