Need formula to recognize blank cells as zero

Hi all,
I got some help on here before for a forumla and I thought it was working great for a while then I realized that when certain cells are left blank it doesnt calculate it properly.
The forumla is perfect except for this one issue, I have attached my spreadsheet which shows the error in cell AJ-172.

I want it to come back with a "0" (Zero) when there is no date range to calculate in a certain quarter.

Any help would be greatly appreciated!!

Does this work for you for cell AJ172?

=MAX(0,MIN(J172,AI172)-MAX(I172,AH172)+1)*(COUNT(I172:J172,AH172:AI172)=4)