static void setArrowImage(ID buttObj, @Nullable Icon arrow) {
    final BufferedImage img = _getImg4ByteRGBA(arrow);
    final Pointer raster4ByteRGBA = _getRaster(img);
    final int w = _getImgW(img);
    final int h = _getImgH(img);
    nstLibrary.setArrowImage(buttObj, raster4ByteRGBA, w, h); // creates autorelease-pool internally
  }
static void setArrowImage(ID buttObj, @Nullable Icon arrow)