Hi. I'm adding a select for the request_rma view and it works but it doesn't make it mandatory. I'm trying to add required="", required="true" or required="required", as usually in html. Is something different to make this in odoo?

select required="required" name="tag_ids" class="form-control o_website_form_select">
    option>---/option>
    t t-foreach="request.env['rma.tag'].sudo().search([], order='id asc')" t-as="tag">
        option t-att-value="tag.id">
	​    ​t t-esc="tag.name"/>
	​​/option>
    /t>
/select>

UPDATE: As I can see, if I use option>---/option> instead of a void text it works but I get a generic error message "An error has occured, the form has not been sent" so it doesn't seem the correct solution. This message is no elegant at all to the user.