This appears to work, however I have the same problem as an above commenter.  I can get the report to run and I can see the list of expenses that have the customer "not specified".  Unfortunately, about half of those expenses actually are specified to a customer:project.  Meaning, when I click on one of them, it has a customer and project assigned to it.  Why those expenses are not showing up on the report under the customer:project is a total mystery to me, and makes the report useless because I still have to go in to every expense to see if it is assigned to a customer or not.