I want to summarize in a single cell at the bottom of the spreadsheet the
results of summing the summed product of multiplying two different columns.

This is the formula I want to write:
=(C12*$U12)+(C13*$U13)+(C14*$U14)+etc., etc.

However, column C cells may not have values in them. If there are no values
the error message #value! comes up. Is there a way to ignore cells without
values and still have all the cells with values sum themselves.

I have also tried this formula, same result:
=IF(D12=1,(D12*$U12)," ")+IF(D13=1,(D13*$U12)," ")

I am trying to avoid inserting a another column (s).

Thanks if your listening!
Roger H.