#vulnerable code 
                             @RequestMapping("/logout")
	public String logout(HttpServletRequest request) {
		HttpSession session = request.getSession();
		
		// 注销本地会话
		if (session != null) {
			session.invalidate();
		}
		
		// 如果是客户端发起的注销请求
		String token = (String) session.getAttribute(AuthConst.TOKEN);
		List<String> clientUrls = authService.remove(token);
		if (clientUrls != null && clientUrls.size() > 0) {
			Map<String, String> params = new HashMap<String, String>();
			params.put(AuthConst.LOGOUT_REQUEST, AuthConst.LOGOUT_REQUEST);
			params.put(AuthConst.TOKEN, token);
			for (String url : clientUrls) {
				AuthUtil.post(url, params);
			}
		}
		// 重定向到登录页面
		return "redirect:/";
	} 
                            #location 11 
                            #vulnerability type NULL_DEREFERENCE
#fixed code
                             @RequestMapping("/logout")
	public String logout(HttpServletRequest request) {
		HttpSession session = request.getSession();
		if (session != null) {
			session.invalidate();
		}
		return "redirect:/";
	}