node.js：req.next不是一个函数

我试图将这个项目部署到谷歌云平台。 代码在我的本地机器上正常工作。 不过，我在gcloud上收到以下错误。

TypeError: req.next is not a function at done (/app/node_modules/express/lib/response.js:955) at tryRender (/app/node_modules/express/lib/application.js:641) at EventEmitter.render (/app/node_modules/express/lib/application.js:591) at ServerResponse.render (/app/node_modules/express/lib/response.js:960) at (/app/routes/posts.js:15) at tryCatcher (/app/node_modules/mongolass/node_modules/bluebird/js/release/util.js:16) at Promise._settlePromiseFromHandler (/app/node_modules/mongolass/node_modules/bluebird/js/release/promise.js:510) at Promise._settlePromise (/app/node_modules/mongolass/node_modules/bluebird/js/release/promise.js:567) at Promise._settlePromise0 (/app/node_modules/mongolass/node_modules/bluebird/js/release/promise.js:612) at Promise._settlePromises (/app/node_modules/mongolass/node_modules/bluebird/js/release/promise.js:691) at Async._drainQueue (/app/node_modules/mongolass/node_modules/bluebird/js/release/async.js:138) at Async._drainQueues (/app/node_modules/mongolass/node_modules/bluebird/js/release/async.js:148) at Immediate.Async.drainQueues (async.js:17) at runCallback (timers.js:666) at tryOnImmediate (timers.js:639) at processImmediate (timers.js:611) 

路线/ posts.js：

 router.get('/', function(req, res, next) { var author = req.query.author; PostModel.getPosts(author) .then(function (posts) { res.render('posts', { //line 15 posts: posts }); }) .catch(next); }); 

getPosts函数：

 getPosts: function getPosts(author) { var query = {}; if (author) { query.author = author; } return Post .find(query) .populate({ path: 'author', model: 'User' }) .sort({ _id: -1 }) .addCreatedAt() .addCommentsCount() .contentToHtml() .exec(); },