private TextBlockBackcolored addLegend(TextBlockBackcolored original) {
    final Display legend = diagram.getLegend();
    if (Display.isNull(legend)) {
      return original;
    }
    final TextBlock text = EntityImageLegend.create(legend, diagram.getSkinParam());

    return DecorateEntityImage.add(
        original, text, diagram.getLegendAlignment(), diagram.getLegendVerticalAlignment());
  }