protected SFont toZssFont(Font poiFont) {
    if (poiFont == null) return null; // ZSS-1138

    SFont font = null;
    final short fontIndex = poiFont.getIndex();
    if (importedFont.containsKey(fontIndex)) {
      font = importedFont.get(fontIndex);
    } else {
      font = createZssFont(poiFont);
      importedFont.put(fontIndex, font); // ZSS-677
    }
    return font;
  }
  protected SFont importFont(CellStyle poiCellStyle) {
    SFont font = null;

    final short fontIndex = poiCellStyle.getFontIndex();
    if (importedFont.containsKey(fontIndex)) {
      font = importedFont.get(fontIndex);
    } else {
      Font poiFont = workbook.getFontAt(fontIndex);
      font = createZssFont(poiFont);
      importedFont.put(fontIndex, font); // ZSS-677
    }
    return font;
  }