code: @Override
      public Enumeration<String> getInitParameterNames() {
          FilterConfig fc = getFilterConfig();
          if (fc == null) {
              throw new IllegalStateException(
                  lStrings.getString("err.filter_config_not_initialized"));
          }
  
          return fc.getInitParameterNames();
      }
docs: <p>Returns the names of the filter's initialization parameters
  as an <code>Enumeration</code> of <code>String</code> objects,
  or an empty <code>Enumeration</code> if the filter has no
  initialization parameters.  See {@link
  FilterConfig#getInitParameterNames}.</p>
  
  <p>This method is supplied for convenience. It gets the
  parameter names from the filter's <code>FilterConfig</code> object.
  
  @return Enumeration 	an enumeration of <code>String</code>
  objects containing the names of
  the filter's initialization parameters
  
  @since Servlet 4.0