Hide only those Select Box which has null value selected

Answer 1

You can use the atrribute selector to find elements that have a selected value :

$('.date-month option[selected="selected"]').parent().hide();

Show/hide selects :

 $('.date-month').each(function() {
    if ($(this).find('option[selected="selected"]').length>0) {
       $(this).hide();
    } else {
       $(this).show();
    }
  });