Hi. I found a bug caused by discount "assigned on order partial total".
This error happen when customer add a product on cart and apply a coupon code that is limited to specific product. if customer remove the product prevoiusly added the discount coupon remain applied (NOP doesn't remove discount if cart is empty). If customer add another product for which the discount is not valid then crash page appear.
For me the problem is generate by an incorrect condition caused by a presence of discount in empty cart: if cart is empty the coupon code must be removed automatically.
MacZ