Can someone tell me why I can't remove my polylines with this code:

```
    $("#chkRouteLines").click(function () {

    var polyline = new google.maps.Polyline({
        path: positions,
        strokeColor: "#FF0000",
        strokeOpacity: 1.0,
        strokeWeight: 2,
        visible: true
    }); ;

    if ($(this).is(':checked')) {
        polyline.setMap(map);
    } else {
        polyline.setMap(null);
    }
})

```

I found in the documentation of google maps api 3 that I need to do: setMap(null)..
But this didn't work.

Thank you!