Need to return null value by default for fields ''Full or Part Time'' & ''Regular or Temporary''

Summary:

I have been trying to set null values by default for fields ''FullPartTime'' & ''Regular&Temporary'' when creating position but it seems that it's not working.

Scenario 1: We put below expressions in respective fields in VBS and it's defaulting to null value for fields ''FullPartTime'' & ''Regular&Temporary'' but throws an error when submitting the position for the both fields.

$fields.positionsV2.FullPartTime.$value(null)

$fields.positionsV2.RegularTemporary.$value(null)

Scenario 2: We then used the setting ''Clear field value'' in VBS and still it doesn't return null value for both fields.

I have prepared the document with all these changes stated above along with screenshots of screen from VBS and Position page.