Saving user roles with new added fulfillment role is not always possible

When I added a new fulfillment role to user and then clicked "Save user roles" button, the notification "Failed to update user roles" is displayed. Saving was not possible. Also, the error message was returned:

Steps to reproduce:
1. Click Administration -> Users
2. Click "Roles" link for user e.g Felix Gwixa
3. Select tab "Fulfillment"
4. Add role for warehouse: Nandumbo Health Center, Role: Warehouse Clerk
5. Click Add role button.
6. Click Save user roles button
7. The notification and message should be visible.

Acceptance Criteria:

• saving a user roles with added fulfillment roles should be possible for every warehouse