if (waypts.options[i].selected == true) {
i insert this line, to Element "waypts" becoming not a mandatory field, but now whole scripts have no funktion.
for (var i = 0; i < waypointstring.length; i++) {
if (waypts.options[i].selected == true) {
waypts.push({location:waypointstring[i], stopover:true});
}
}
Finally found the solution :
var address = waypointstring[i];
if (address !== "") {
here is the whole source example