Commerce Manager: Deleting order payment throws error

Description

Steps to reproduce

1. Go to Commerce Manager.
2. Create a new order.
3. Add a line item to the order -> Click Save Order.
4. Add a Payment to the order.
5. Delete the payment > Click Save or/Cancel button > Nothing happens.
6. Open the order again.

Expected: The order is saved, and the cancel action is successful.

Actual result: It shows the error below.

[NullReferenceException: Object reference not set to an instance of an object.]
Mediachase.Commerce.Manager.Order.CommandHandlers.PurchaseOrderHandlers.DeleteSelectedPaymentHandler.IsCommandEnable(IOrderGroup order, CommandParameters cp) +428
Mediachase.Commerce.Manager.Apps.Order.CommandHandlers.OrderGroupHandlers.OrderGroupCommandHandlerBase.IsEnable(Object sender, Object element) +111
Mediachase.BusinessFoundation.CommandHandler.IsCommandEnableHandler(Object Sender, Object Command, Object Argument) +650
Mediachase.BusinessFoundation.CommandManager.IsEnable(String commandName, Dictionary`2 listParams) +306
Mediachase.BusinessFoundation.CommandManager.AddCommand(String className, String viewName, String placeName, CommandParameters cp, Boolean& isEnabled) +281