Filter 'Unassigned' Tests for the field 'Assignee' in Test Repository throwing error

Description:

Filter 'Unassigned' Tests for the field 'Assignee' in the Test Repository throwing error as "The value '_unassigned_' does not exist for the field assignee"

Pre-conditions:

Create folders in the Test Repository and add some Unassigned Tests in the folders.

How to reproduce

1. Navigate to a folder in the test repository
2. Click on the 'Filters' button
3. Click on the 'More' button
4. Tick the 'Assignee' option and hit 'Set'
5. Select 'Unassigned' in the 'Assignee' dropdown
6. Hit 'Apply'

Actual result/Attachments:{}

Instead of returning the Unassigned Test cases from the folders, it is throwing an error as " The value 'unassigned' does not exist for the field assignee"

Expected result:

When filtering the 'Assignee' field value as 'Unassigned', it should return the Unassigned Tests from the folder in the Test repository.