Extra rows in redeemed coupon table on checkout form

On the coupon redemption pane on the checkout page, once you've entered a coupon to redeem, it displays a little table of all coupons being applied to the order so far. This table ends up with a bunch of extra empty rows.

The problem is in commerce-coupon-redemption-form.html.twig, where the twig filter function is being used incorrectly (by default it will filter on array value, and the array key is passed as a second parameter).