Incorrectly managed «select list (single choice)» custom fields

I've created a custom field of type «select list (single choice)» and configured on a ServiceDesk item as required.

The behaviour observed is that the first item is automatically selected and therefore the mandatory requirement will be always honoured. Unfortunately this behaviour tends to collect wrong values from the user…

The behaviour expected is that the input field is empty OR prompted with a «none» option… so to force the user to select the appropriate value