code: @Override
    protected boolean beforeExport() {
      if (null == titles) {
        String contextTitle = context.get("titles", String.class);
        if (null != contextTitle) {
          titles = Strings.split(contextTitle, ",");
        }
      }
      if (null == titles || titles.length == 0) return false;
      writer.writeTitle(null, titles);
      return true;
    }
docs: {@inheritDoc}