docs: String getCategoryFilter() {
  
          String result = "";
          if (!m_config.getCategories().isEmpty()) {
              List<String> categoryVals = Lists.newArrayList();
              for (String path : m_config.getCategories()) {
                  try {
                      path = CmsCategoryService.getInstance().getCategory(
                          m_cms,
                          m_cms.getRequestContext().addSiteRoot(path)).getPath();
                      categoryVals.add("\"" + path + "\"");
                  } catch (CmsException e) {
                      LOG.warn(e.getLocalizedMessage(), e);
                  }
              }
              if (!categoryVals.isEmpty()) {
                  String operator = " " + m_config.getCategoryMode() + " ";
                  String valueExpression = CmsStringUtil.listAsString(categoryVals, operator);
                  result = "&fq=category_exact:(" + valueExpression + ")";
  
              }
          }
          return result;
      }