I think we have an original problem’s new brother here:
If I try to sum these columns and some ones are empty (blank), the result is wrong
Qt1*Pr1 + Qt2*Pr2 + 1

this example can guide you to understand the cases with problems:

the trick works:
IF {MyColumn} is empty THEN 0 ELSE {MyColumn}
but I have more than 10 columns and don´t want to duplicate these data dummy every time I find this case. Can it can be fixed and avoid the workaround?
Thanks!
Feliz día.