Sumproduct - ignore blank cells

Hi,

I have a sumproduct formula which I need help with if possible...

The formula:
=SUMPRODUCT((Budget!$A$3:$A$16=$B$3)*(Budget!$B$3:$B$16=$C$4)*(Budget!$C$2:$D$2=$B6)*(Budget!$C$3:$D$16))

Works providing there is no blank cells on the budget sheet column C however due to my data is exported this column will always be blank.

Is there any way in which I can amend the formula to ignore blank cells. I know I can change the array but I do not want to do this as in my data I have other instances where I have blank cells.

Regards

Paul