Hey Doug,
You could create a synthetic coloumn equal to the coloumn where you see blanks instead of zeros. When you create it you will see the options to make it a number and to make it summable.
Steps:
Click on the table where you have the data
Click on the data tab when the ad hoc query pops up and choose insert formula coloumn
Make the formula equal to the coloumn with the data in it that has blanks OR use the numeric value option if it is a metric
Choose the correct configuration of the coloumn so it is a number or currency and it is summable
This should work for what you are looking for but Justin is right. If it is a number format in the data it should have 0's instead of blanks so double check that to.

Let me know if you have any questions about this!
Thanks,
Lauren