After upgrading EPiServer Commerce from 9.6.0 to 9.8.1 I got some breaking changes in new Promotions. I figured out how to make it work, but I am not sure if it's correct way. 

First of all, implementing PromotionProcessor by inheriting from PromotionProcessorBase<> now has different abstract method:

RewardDescription Evaluate(IOrderForm orderForm, AdditionalDiscountPromoData promotionData, PromotionProcessorContext context)

Now it returns RewardDescription instead of IPromotionResult. It seems that I can keep my logic, but have to construct new RewardDescription. It has nice factory methods for different cases:

• CreatePercentageReward
• CreateFreeItemReward
• CreateMoneyReward

Only missing method is when constructing response for no reward (not fulfilled). So I am doing it myself:

private RewardDescription NoReward(PromotionData promotionData)
{
	return new RewardDescription(
			FulfillmentStatus.NotFulfilled, 
			Enumerable.Empty(), 
			promotionData, 
			unitDiscount: 0,
			unitPercentage: 0, 
			rewardType: RewardType.None, 
			description: "No discount applied");
}

The resulting code is here:

public override RewardDescription Evaluate(
	IOrderForm orderForm, 
	AdditionalDiscountPromoData promotionData,
	PromotionProcessorContext context)
{
	var cart = context.OrderGroup as Cart;
	if (cart == null)
	{
		return NoReward(promotionData);
	}

	var additionalDiscountPercent = (decimal)(cart[Constants.AdditionalDiscountPercentMetaField] ?? 0.0m);
	if (additionalDiscountPercent == 0)
	{
		return NoReward(promotionData);
	}

	if (!orderForm.Shipments.Any()) // Shipment gets removed when no items in the cart
	{
		return NoReward(promotionData);
	}

	var affectedItems = orderForm.Shipments
								.First()
								.LineItems
								.Select(lineItem => new AffectedItem(LineItemContentLink(lineItem), lineItem));

	return RewardDescription.CreatePercentageReward(
								FulfillmentStatus.Fulfilled, 
								affectedItems, 
								promotionData, 
								additionalDiscountPercent, 
								description: $"{additionalDiscountPercent} % discount applied to order");
}

private ContentReference LineItemContentLink(ILineItem lineItem)
{
	return _referenceConverter.GetContentLink(lineItem.Code);
}

private RewardDescription NoReward(PromotionData promotionData)
{
	return new RewardDescription(
			FulfillmentStatus.NotFulfilled, 
			Enumerable.Empty(), 
			promotionData, 
			unitDiscount: 0,
			unitPercentage: 0, 
			rewardType: RewardType.None, 
			description: "No discount applied");
}

This works, but has some issues.

Promtions doesn't get removed from DB when you change promotion amount - old promotion's SavedAmount gets set to 0.

Also when you remove an item form the cart, shipment gets removed too - so you have to always check if Shipment exists in Evaluate method.

The questions are:

- How to make promotions get removed from DB? While it functions properly, it keeps unnecessary records in DB.

- Why shipment gets removed after all items removed from cart?

- Could RewardDescription.NoReward() factory method get added to newer version of Promotions?