saveCurrentUser 报错

我是在express框架上开发的，当用到登录功能时，碰到了这个问题：

res.saveCurrentUser is not a function

我已经启用了启用了 CookieSession 中间件了。SDK是最新版的。

报错信息：

res.saveCurrentUser is not a function

TypeError: res.saveCurrentUser is not a function
at D:\nodejs\bsztc\routes\app\users.js:23:9
at wrappedResolvedCallback (D:\nodejs\bsztc\node_modules\leanengine\node_modules\leancloud-storage\dist\node\promise.js:391:40)
at D:\nodejs\bsztc\node_modules\leanengine\node_modules\leancloud-storage\dist\node\promise.js:320:24
at Function._.each._.forEach (D:\nodejs\bsztc\node_modules\underscore\underscore.js:153:9)
at Promise.resolve (D:\nodejs\bsztc\node_modules\leanengine\node_modules\leancloud-storage\dist\node\promise.js:319:7)
at Promise.<anonymous> (D:\nodejs\bsztc\node_modules\leanengine\node_modules\leancloud-storage\dist\node\promise.js:404:27)
at Promise.wrappedResolvedCallback (D:\nodejs\bsztc\node_modules\leanengine\node_modules\leancloud-storage\dist\node\promise.js:391:40)
at D:\nodejs\bsztc\node_modules\leanengine\node_modules\leancloud-storage\dist\node\promise.js:468:33
at _combinedTickCallback (internal/process/next_tick.js:67:7)
at process._tickDomainCallback (internal/process/next_tick.js:122:9)

我是按照demo上操作的，已经加载了的