You are right that would be an example of a bond/bill with a 0% coupon rate. There are still weird negative interest rate conditions where it makes sense to buy an IOU for more than you get back (not that I understand those conditions :) )
I think the 'weird' conditions are some combination of there not being other 'riskless' (or less risky) investments and certain institutions being legally required to hold a certain number or amount of 'riskless' or highly-rated (according to the relevant regulators) instruments.