Genuine question: What are the legitimate uses of $0 invoices? The only thing I can think of is a product that usually costs money (and thus has an invoice workflow), but has been marked as free for some promotion.
I sold a product and it was paid for by gift certificate or a special promo. I want to send a $0.00 invoice for the customer to see it and enjoy the feeling (Sweet! Free jerky/flowers/socks). It's great marketing and the customer will remember you the next time they want some jerky/flowers/socks.
Clarity of expression is a superpower
I don’t feel it’s pedantic at all.