I actually got two of these messages while I was out for the holiday break. I don't work on the team that handles invoicing; but, I (among others) made them aware of this issue and they are definitely working on a fix.
The challenge, of course, is that there are plenty of legitimate reasons for sending $0 invoices and we don't want to artificially make our product worse for our many legitimate customers by going too far in trying to stop this spam.