code: private static void embedDarkDotAtLeftBottomCorner(ByteMatrix matrix) throws WriterException {
      if (matrix.get(8, matrix.getHeight() - 8) == 0) {
        throw new WriterException();
      }
      matrix.set(8, matrix.getHeight() - 8, 1);
    }
docs: Embed the lonely dark dot at left bottom corner. JISX0510:2004 (p.46)