[development] Hidden required select field with default value

Hello, I'm trying to modify a form where I'm hiding a select field. This field is usually required. When setting the #type = hidden The field is hidden, but when trying to submit the form I get an error about the fields being required. Looking at the $form dump, I see that the select field has a default value. (a term id). I tried changing the Required to false when hiding but then the field looses its value. Is there some other property I need to set? Thanks Idan