static BufferedImage tilesToImage_twoLevelList(LL<BufferedImage> tiles) {
  if (empty(tiles)) null;
  int columns = maxLength(tiles);
  int rows = l(tiles);
  int w = intSum(mapMethod getWidth(first(tiles)));
  int h = intSum(mapMethod getWidth(map first(tiles)));
  BufferedImage img = newBufferedImage(w, h);
  
  int yy = 0;
  for y to rows: {
    int xx = 0, th = 0;
    for x to columns: {
      BufferedImage tile = get(tiles.get(y), x);
      if (tile != null) {
        copyBufferedImage(tile, img, xx, yy);
        xx += tile.getWidth();
        th = tile.getHeight();
      }
    }
    yy += th;
  }
  ret img;
}