It really should not be possible to define a cost for an item that has no inventory unit of measure. This is a major loop hole. if you don't realize your item is missing inventory unit of measure, and you set a cost, the item will never transact, obviously. You can't fix the unit either because the item already has a cost. The item has to be deleted. This has to be impossible. When the user is about to activate a cost for an item without Inventory UofM, a showstop warning should occur.