code: private String getValidLogoutExitPage(HttpServletRequest req) {
  
          boolean valid = false;
          String exitPage = req.getParameter("logoutExitPage");
          if (exitPage != null && exitPage.length() != 0) {
              boolean logoutExitURLaccepted = verifyLogoutURL(req, exitPage);
              if (logoutExitURLaccepted) {
                  exitPage = removeFirstSlash(exitPage);
                  exitPage = compatibilityExitPage(req, exitPage);
                  valid = true;
              }
          }
          return valid == true ? exitPage : null;
      }
docs: return a logoutExitPage string suitable for redirection if one is defined and valid.
  else return null