if (id == null) throw new NullPointerException("Expecting a not-null id.");
if (pixels == null) throw new NullPointerException( "Expecting a not-null pixels element.");
    public PixelBuffer (Integer id, Pixels pixels)    {        if (id == null)            throw new NullPointerException("Expecting a not-null id.");                this.pixels = pixels;        this.id = id;        path = Helper.getPixelsPath(id);    }