Reference variables in Service Portal don't show records of target table whose 'display' column values are empty

Identified in Jakarta and Kingston releases so far.

1. Open an OOB Kingston instance.

2. Create a test catalog item in sc_cat_item table (Maintain Items).

3. Post creating new created catalog item, under "Variables" related list create a new variable (by clicking "New") and enter the following details:
Question: User
Name: User
Reference: User [sys_user]
Use reference qualifer: Simple
Reference qualifier condition: [User ID] [is empty]

4. The above reference field with the above reference qualifier will show only those records whose User IDs are empty. So let's create some test users like that.

5. Under sys_user table, kindly create the following test users:
UserID: <empty>
First Name: Test
Last Name: User1
Email: test.user1@example.com
-------------------------------------------
UserID: <empty>
First Name: Test
Last Name: User2
Email: test.user2@example.com
-------------------------------------------
UserID: <empty>
First Name: Test
Last Name: User2
Email: test.user3@example.com

6. Since sys_user table is the target table for the reference field, we need to set a display column of this table. So go to sys_dictionary table and open the record of table 'sys_user' and column name 'user_name' (User ID).

7. Set Display as 'true'. Save it. This ensures that the User ID field will be the displaying field for the reference variable.

8. Now go to Service Portal and open this catalog item via /sp?id=sc_cat_item&sys_id=<sys_id_of_new_catalog_item>

9. You will see the reference field "User" won't be showing any records (though we have three records).

Expected: should show <empty> records.
Actual: Shows "No Matches Found". Doesn't show any records.

The workarounds are:
- Set display as true for a different column.
- Or if you don't want to do option 1 then use Lookup Select box instead of reference type variable.