code: public static String validateAttributeNames(
        Enumeration<String> attributeNames) {
      while (attributeNames.hasMoreElements()) {
        String attribute = attributeNames.nextElement();
        if (!attribute.equals("users") && !attribute.equals("poolGroups") &&
            !attribute.equals("poolInfos") && !attribute.equals("toKillSessionId")
            && !attribute.equals("killSessionsToken")) {
          return 
            "Illegal parameter " + attribute + ", only 'users, " +
            "poolGroups, 'poolInfos', 'toKillSessionId' and 'killSessionsToken'" +
            "parameters allowed.";
        }
      }
      return null;
    }
docs: Check the attribute names
  @param attributeNames Atttribute names to check
  @return Null if all attribute names are invalid, non-empty if the check
  failed, with an appropriate error message