Radio buttons custom field set as Optional still shows "None" as an option in Portal

Issue Summary

Radio buttons custom field set as Optional keeps showing "None" as an option even if the customer has a Default Value set.

This is similar to JRACLOUD-75541 but it affects Customer Portal directly.

Steps to Reproduce

1. Create a radio button custom field and add some options.
2. Don't select any Default Value for it
3. Add the field to a screen and keep the field as Optional
4. Add this radio button to a Request Type
5. You'll see the 'None' option showing in your Customer Portal

Expected Results

There is no reason to show the None option if the user didn't create one.

Actual Results

You'll see a 'None' option showing for users:

Workaround

If you set the Radio Button field as Required, you will not see the None option anymore in your Portal