Make Work Notes as Mandatory when Assignment Group is Changed on Incident Form

function onChange(control, oldValue, newValue, isLoading, isTemplate) {
 if (isLoading || newValue == '' || oldValue == '') {
  return;
 }
 g_form.flash("incident.work_notes", "#FFFCCC", -4);
 g_form.setMandatory("work_notes", true);
 g_form.addInfoMessage("Please enter work notes when changing assignment groups.");
}