Adding point features to an existing FeatureLayer

I have a FeatureLayer (point) to which I would like to digitize some points and add them to this layer. The FeatureLayer can have some attributes, e.g fid (int, primary key), Name (string) and the_geom (point geometry)...

I've tried to read the original features and add them to a FeatureCollection (array list). Then I'm trying to add my new digitized points to this array, and create a new FeatureLayer with this featureCollection. I can't get it to work. New features are added but the point-geometry is stored in the Name attribute as a WKT-String (POINT (15.026579830870883 58.37316178562563)) and has no geometry, the primary key for the new points are correct.

This is my current faulty function for adding new points:

static void addNewPoints(Coordinate[] coordinates) {
    
    SimpleFeatureType sft=(SimpleFeatureType) layer.getFeatureSource().getSchema();
    SimpleFeatureBuilder builder = new SimpleFeatureBuilder((SimpleFeatureType) sft);
    GeometryFactory geometryFactory = JTSFactoryFinder.getGeometryFactory();
    Point point;
    Style style = null;
    List<SimpleFeature> featureCollection = new ArrayList<>();
    if (layer!=null && layer.getFeatureSource()!=null) {
        style = layer.getStyle();
        //Add existing features to the feature collection
        try {
            FeatureIterator<SimpleFeature> fi= (FeatureIterator<SimpleFeature>) 
                       layer.getFeatureSource().getFeatures().features();
            while(fi.hasNext()) {
                featureCollection.add((SimpleFeature)fi.next());
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    // Add the new points to the existing points
    for (int i = 0; i<coordinates.length; i++) {

        // ??? what shall the argument be ???
        SimpleFeature feature = builder.buildFeature(null);
        
        if (CRS.getAxisOrder(MapView.map.getCoordinateReferenceSystem())
                 .equals(AxisOrder.EAST_NORTH)) {
            point = geometryFactory.createPoint(new Coordinate(coordinates[i].x,
                    coordinates[i].y));
        } else {
            point = geometryFactory.createPoint(new Coordinate(coordinates[i].y,
                    coordinates[i].x));
        }
        builder.add(point);
        featureCollection.add(feature);
    }
    layer = new FeatureLayer(DataUtilities.collection(featureCollection), style);
    layer.setTitle("Tmp_"+ sft.getName().toString());
    addLayerToTheMap(layer);
}