#VALUE! error on ROUND function

I need to add the ROUND function to my formula, but when I do, there will be a #VALUE! error in every cell where S2502 is empty. It works fine with the ROUND function in there, providing S2502 is populated.

Without the ROUND formula in there, it works perfectly in all the cells whether S2502 is blank or not. So I obviously need to tweak the formula a bit but I cannot seem to get it quite right.

=ROUND(IF(S2502="","",S2502*Q2502*R2502),2)