code: static void throwIfUnrecognizedParamName(Enumeration initParamNames) throws ServletException {
          final Set<String> recognizedParameterNames = new HashSet<String>();
          recognizedParameterNames.add(ALLOW_MULTI_VALUED_PARAMETERS);
          recognizedParameterNames.add(PARAMETERS_TO_CHECK);
          recognizedParameterNames.add(CHARACTERS_TO_FORBID);
  
          while (initParamNames.hasMoreElements()) {
              final String initParamName = (String) initParamNames.nextElement();
              if (!recognizedParameterNames.contains(initParamName)) {
                  throw new ServletException(
                          "Unrecognized init parameter ["
                                  + initParamName
                                  + "].  Failing safe.  Typo"
                                  + " in the web.xml configuration? "
                                  + " Misunderstanding about the configuration "
                                  + RequestParameterPolicyEnforcementFilter.class.getSimpleName()
                                  + " expects?");
              }
          }
      }
docs: Examines the Filter init parameter names and throws ServletException if they contain an
  unrecognized init parameter name.
  
  <p>This is a stateless static method.
  
  <p>This method is an implementation detail and is not exposed API. This method is only
  non-private to allow JUnit testing.
  
  @param initParamNames init param names, in practice as read from the FilterConfig.
  @throws ServletException if unrecognized parameter name is present