How to reproduce :
- in a form, insert a select field
- Do not define any placeholder, do not declare this one as mandatory field
<select id="Ametys_Gen_2" name="select1" style="width: 100px;"><option disabled="disabled" selected="selected"></option><option> </option><option value="valeur_1">Choix affiché 1</option><option value="valeur_2">Choix affiché 2</option><option value="valeur_3">Choix affiché 3</option></select>