500 Server Error when a new subscriber tries to save list-options without selecting a button for all settings

For a new member visiting her list-options page with no individual options yet set, the radio buttons are all unselected. If the form is then POSTed without selecting a setting for each option, the options with no selection are submitted with invalid values.

I'm not sure if this occurs with any option unselected, but it definitely occurs when Delivery status is unselected resulting in "HTTP Error 400: Cannot convert parameters: delivery_status" from REST which in turn results in the 500 Server Error to the user.