Unexpected error occurs after submitting Settings form without selecting a redirect location.
1. Add Form block.
2. Open settings.
3. In Confirmation section switch from Thank you message to Redirect to location.
4. Do not select a location.
5. Click Save form.
Actual: Unexpected error occurs.
Expected: Select button is set to mandatory like in e.g. Contentlist block (attached).
Remarks: Attached exception from log.