Description
Steps to reproduce:
1. Create a client with Legal Form=Entity and assign this client a value from the Main Business Line. Save.
2. Edit this client and try to remove Main Business Line (assign back to --Select Main Business Line). Save.
3. Edit again and observe Main Business Line is still assigned.
Seems to be an issue for Client Nonperson domain object, as other drop downs related to Client domain object are working as expected.