A discount greater than the product's price generates a negative cart amount

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.1.4
• Fix Version/s: 2.1.0
• Component/s: Digital Merchandise Management → Discounts
• Labels: None
• Git Pull Request: https://github.com/marco-leo/liferay-portal-ee/pull/258

Steps to Reproduce

1. Create a new user
2. Create a Breccia site for convenience
3. Go to Commerce → Discounts
4. Create a new entry
5. Type a name
6. Select "Apply to Total" as type
7. Select User as User Segment
8. Flag "Use Coupon Code"
9. Type a Code
10. Unflag "Percentage"
11. Type an amount (e.g. 1)
12. Flag "Active"
13. Publish
14. Log in as a non-admin user
15. Go to Catalog
16. Add to cart a product which price is lower than $ 1.00 (SKU 1101667 - $ 0.73)
17. Go to the mini cart → Edit Cart
18. Enter the promo code inserted at point 8
19. Click Apply

Expected Behavior

The Total should be 0 or greater

Actual Behavior

Since it's permitted to create a discount without defining a Rule, as you can see from the screenshot, the cart amount after applying the discount is $ -0.27.