[GK] Exclude Update-Only Field From Select

### Overview
This branch fixes an issue with the Invoice model where a write only field was being pulled back in the select thus causing errors.  I added the field to the list of write only fields so it won't be pulled back.  

### Testing
Only real way I can think to test this would be to build up a little sample app and pull back invoices for a user which would fail prior to the change.  Otherwise we can just test it with some of the BOSS code since that what this fixes.