Hi.

When perform billing is done on a request, we sometimes have zero cost non-parts and parts.

This creates vouchers that go into error because the cost set to zero. For Non-parts I made a workaround to delete zero cost lines on the non_part_usage table. However I can not do the same for the parts, because it needs to stay as is for various reasons. 

My question: Is there a built in function to stop vouchers from being created for something that obviously is going to cause an error by not costing anything? What is the default method for handling this?