TypeError: E:\movie-master\app\views\pages\detail.jade:13
   11|           .panel-body
   12|             ul.media-list
 > 13|               each item in comments
   14|                li.media
   15|                  .pull-left
   16|                    a.comment(href="#comments", data-cid="#{item._id}", data-tid="#{item.from._id}")

Cannot read property 'length' of undefined
   at eval (eval at <anonymous> (E:\movie-master\node_modules\jade\lib\index.js:218:8), <anonymous>:467:31)
   at eval (eval at <anonymous> (E:\movie-master\node_modules\jade\lib\index.js:218:8), <anonymous>:876:4)
   at eval (eval at <anonymous> (E:\movie-master\node_modules\jade\lib\index.js:218:8), <anonymous>:1066:22)
   at res (E:\movie-master\node_modules\jade\lib\index.js:219:38)
   at Object.exports.renderFile (E:\movie-master\node_modules\jade\lib\index.js:380:38)
   at Object.exports.renderFile (E:\movie-master\node_modules\jade\lib\index.js:370:21)
   at View.exports.__express [as engine] (E:\movie-master\node_modules\jade\lib\index.js:417:11)
   at View.render (E:\movie-master\node_modules\express\lib\view.js:128:8)
   at tryRender (E:\movie-master\node_modules\express\lib\application.js:640:10)
   at EventEmitter.render (E:\movie-master\node_modules\express\lib\application.js:592:3)
   at ServerResponse.render (E:\movie-master\node_modules\express\lib\response.js:971:7)
   at E:\movie-master\app\controllers\movie.js:13:20
   at E:\movie-master\node_modules\mongoose\lib\query.js:2843:9
   at process._tickCallback (internal/process/next_tick.js:109:7)

这是为什么？？