Currently if you add a field in the fields parameter with a wildcard, no fields will be added to the hits layer. The situation is even worst if the wildcard matches the field name of the geo_point or geo_shape field, in that case a ClassCastException is thrown.
x-pack/plugin/vector-tile/src/javaRestTest/java/org/elasticsearch/xpack/vectortile/VectorTileRestIT.java
private void assertBucketKeyTag(VectorTile.Tile.Layer layer, VectorTile.Tile.Feature feature) {
        for (int i = 0; i < feature.getTagsCount(); i += 2) {
            String thisTag = layer.getKeys(feature.getTags(i));
            if ("_key".equals(thisTag)) {
                VectorTile.Tile.Value thisValue = layer.getValues(feature.getTags(i + 1));
                
                GeoTileUtils.longEncode(thisValue.getStringValue());
                return;
            }
        }
        fail("Could not find tag [|_key]");
    }
    private VectorTile.Tile execute(Request mvtRequest) throws IOException {
        final Response response = client().performRequest(mvtRequest);
        final InputStream inputStream = response.getEntity().getContent();
        assertThat(response.getStatusLine().getStatusCode(), Matchers.equalTo(HttpStatus.SC_OK));
        return VectorTile.Tile.parseFrom(inputStream);
    }
    private VectorTile.Tile.Layer getLayer(VectorTile.Tile tile, String layerName) {
        for (int i = 0; i < tile.getLayersCount(); i++) {
            final VectorTile.Tile.Layer layer = tile.getLayers(i);
            if (layerName.equals(layer.getName())) {
                return layer;
            }
        }
        fail("Could not find layer " + layerName);
        return null;
    }
}