Event after modifying polygon in Google Maps API v3

I made a mapping application that uses the drawing manager (and implements selectable shapes). The program works as follows: when finishing drawing the polygon after clicking a button a path, is mapped on the polygon.

When the polygon is edited after this process I want the mapping function to be called again. However I can't get this part working:

I tried using following code, but I always get an error because no shape is selected yet when this listener is added. What can I do?

google.maps.event.addListener(selectedShape, 'set_at', function() {
    console.log("test");
});

google.maps.event.addListener(selectedShape, 'insert_at', function() {
    console.log("test");
});

Important pieces of code:

function showDrawingManager(){
    var managerOptions = {
        drawingControl: true,
        drawingControlOptions: {
            position: google.maps.ControlPosition.TOP_CENTER,
            drawingModes: [google.maps.drawing.OverlayType.MARKER, google.maps.drawing.OverlayType.POLYLINE, google.maps.drawing.OverlayType.POLYGON]
        },
        markerOptions: {
            editable: true,
            icon: '/largeTDGreenIcons/blank.png'
        },
        polygonOptions: {
            fillColor: "#1E90FF",
            strokeColor: "#1E90FF",
        },
        polylineOptions: {
            strokeColor: "#FF273A"
        }
    }

    var drawingManager = new google.maps.drawing.DrawingManager(managerOptions);
    drawingManager.setMap(map);
    return drawingManager;
}

function clearSelection() {
    if (selectedShape) {
        console.log("clearSelection");

        selectedShape.setEditable(false);
        selectedShape = null;
        numberOfShapes--;
    }
}

function setSelection(shape) {

   console.log("setSelection");

   clearSelection();
   selectedShape = shape;
   shape.setEditable(true);
   numberOfShapes++;
   //getInformation(shape);
}

function initialize(){

    //....

    var d