public ObjectProperty<MapProvider> mapProviderProperty() {
        if (null == mapProvider) {
            mapProvider = new ObjectPropertyBase<MapProvider>(_mapProvider) {
                @Override protected void invalidated() { fireTileEvent(MAP_PROVIDER_EVENT); }
                @Override public Object getBean() { return Tile.this; }
                @Override public String getName() { return "mapProvider"; }
            };
            _mapProvider = null;
        }
        return mapProvider;
    }
Defines an optional node that can be used in combination with the
CustomTileSkin.
@param GRAPHIC
src/main/java/eu/hansolo/tilesfx/Tile.java