Can't update the kit unpack list.
*Reproduction steps: *
1. As administrator go to Administration -> Products and click “Edit” next to any product
2. Select Kit Unpack List tab
3. Click "Add Products"
4. Select a few products and click "Add Products"
5. Fill the Quantity input fields
6. Click "Save Kit Unpack List"
7. Error appears (status code 500)
A notification stating that the kit unpack list had been updated successfully should appear, and one should return to the Products screen.