docs: public static String appendParameter(String url, String paramName, String paramValue) {
  
          if (CmsStringUtil.isEmpty(url)) {
              return null;
          }
          int pos = url.indexOf(URL_DELIMITER);
          StringBuffer result = new StringBuffer(256);
          result.append(url);
          if (pos >= 0) {
              // url already has parameters
              result.append(PARAMETER_DELIMITER);
          } else {
              // url does not have parameters
              result.append(URL_DELIMITER);
          }
          result.append(paramName);
          result.append(PARAMETER_ASSIGNMENT);
          result.append(paramValue);
          return result.toString();
      }