ol4.2 wfs layer not showing on map

Question

I looked at this example to load a layer into my map. I get a response from my geoserver in geoJSON format. But still, the layer is not showing on my map. I also zoomed out to check for reprojection issues. No error is thrown in console.

When I parse my response in http://geojsonlint.com/ the response is:

Line 1: old-style crs member is not recommended
Line 1: Polygons and MultiPolygons should follow the right-hand rule 

But http://geojson.io shows the geoJSON fine.

My Code:

var vectorSource = new ol.source.Vector({
    format: new ol.format.GeoJSON(),
    url: function(extent) {
      return 'http://192.168.66.110:8080/geoserver/gis/ows?service=WFS&version=1.1.0&request=GetFeature&typeName=gis:tbl_krs&outputFormat=application/json&srsname=EPSG:4326&'+
          'bbox=' + extent.join(',') + ',EPSG:3857';
    },
    strategy: ol.loadingstrategy.bbox
  });

var wfsLayer =  new ol.layer.Image({
        source: new ol.source.ImageVector({
          source: vectorSource
        })
})

map.addLayer(wfsLayer)
wfsLayer.setVisible(true);

Also my map and view settings:

var view = new ol.View({
    center: ol.proj.fromLonLat([10, 51]),
    zoom: 6
});

var map = new ol.Map({
target: 'map',
view: view,
controls: ol.control.defaults().extend([
    new ol.control.Zoom(),
    //new ol.control.FullScreen(),
    //new ol.control.ZoomSlider(),
    new ol.control.LayerSwitcher({  
        tipLabel: 'Layer Switcher'
    }),
    //new ol.control.OverviewMap(),
    new ol.control.ScaleLine()
]),
layers: [baselayers, toplayers]
});

Response snippet with &srsname=EPSG:3857:

{
"type": "FeatureCollection",
"totalFeatures": 402,
"features": [{
    "type": "Feature",
    "id": "tbl_krs.155",
    "geometry": {
        "type": "MultiPolygon",
        "coordinates": [
            [
                [
                    [729476.78514853, 6399530.92085941],
                    [730019.30907858, 6400235.09490534],
                    [729750.34332383, 6401154.79413948],
                    [732440.10602656, 6404204.80738186],
                    [734470.17505526, 6403726.40499375],
                    [735141.6145631, 6404055.5354657],
                    [736018.53227221, 6405097.25241155],
                    [736425.08527793, 6405666.89631325],
                    [736099.05752955, 6406241.17954547],
                    [734876.82520048, 6406485.23386293],
                    [734452.09336458, 6407838.53494448],
                    [738103.00414279, 6409743.87439966],
                    [741458.74796937, 6415323.4007552],
                    [742925.10037322, 6421025.93818922],
                    [744970.38199679, 6421488.71771255],
                    [746284.45642492, 6420160.14779568],
                    [746381.92207616, 6420014.33618437],
                    [748759.03462201, 6413394.73771304],
                    [750198.42322968, 6408846.9377395],
                    [750145.83936406, 6407601.8344375],
                    [747610.81232342, 6406668.48474281],
                    [745235.97782396, 6404472.83499567],
                    [746748.34292771, 6403300.16004243],
                    [749183.2598718, 6401116.61335638],
                    [747061.97817989, 6398076.58747616],
                    [745423.93817996, 6396189.48940849],
                    [739740.91688288, 6394589.86928475],
                    [736242.45634245, 6394315.09502095],
                    [735958.35722326, 6394805.50239602],
                    [735501.96048888, 6397678.32572755],
                    [731921.89800399, 6395833.91169814],
                    [730488.39371686, 6396786.80690645],
                    [730086.93440624, 6397467.86745722],
                    [729476.78514853, 6399530.92085941]
                ]
            ]
        ]
    },
    "geometry_name": "the_geom",
    "properties": {
        "krs": "Trier",
        "sumarea_3": 0,
        "sumarea_5": 0,
        "bl": "Rheinland-Pfalz",
        "sumarea_1": 0,
        "sumarea_1_": 2404,
        "sumarea_3_": 1713,
        "sumarea_5_": 663
    }
}],
"crs": {
    "type": "name",
    "properties": {
        "name": "urn:ogc:def:crs:EPSG::3857"
    }
}
}

EDIT:

I can see the layer by using this code, but that's not what I need:

var wfsVectorLayer = new ol.layer.Vector({
        source: vectorSource

});

map.addLayer(wfsVectorLayer)
wfsVectorLayer.setVisible(true);

EDIT 2:

wfsLayer.getSource().getSource().getFeatures()

is returning my features too.

Should I create a ticket at OpenLayers' github at this point?

Answer 1

Finally found the solution: I had to specify a style. I thought that OpenLayers would choose a standard style if none was specified or at least would throw a warning sign at me.

var vector = new ol.layer.Image({
  source: new ol.source.ImageVector({
    source: vectorSource,
    style: featureStyleFunction
  })
});