Can't call method 'call' of undefined

[Thomas de Zeeuw]

When I first request the page I get the correct response, however the second request I get a 500 response.

app.use(function* (next) {
  // Array with middleware functions,
  // generated elsewhere, but on every request
  var mws = [];

  yield compose(mws);

  yield next;
});

Error stack:

TypeError: Cannot call method 'call' of undefined
at Object. (/Users/thomas/CloudStation/Dropbox/www/koa-router/node_modules/koa-compose/index.js:36:19)
at GeneratorFunctionPrototype.next (native)
at next (/Users/thomas/CloudStation/Dropbox/www/koa-router/node_modules/koa/node_modules/co/index.js:76:21)
at Object. (/Users/thomas/CloudStation/Dropbox/www/koa-router/node_modules/koa/node_modules/co/index.js:56:5)
at next (/Users/thomas/CloudStation/Dropbox/www/koa-router/node_modules/koa/node_modules/co/index.js:92:21)
at Object. (/Users/thomas/CloudStation/Dropbox/www/koa-router/node_modules/koa/node_modules/co/index.js:56:5)
at Server. (/Users/thomas/CloudStation/Dropbox/www/koa-router/node_modules/koa/lib/application.js:105:8)
at Server.EventEmitter.emit (events.js:101:17)
at HTTPParser.parserOnIncoming as onIncoming
at HTTPParser.parserOnHeadersComplete (_http_common.js:111:23)

[Thomas de Zeeuw]

For some reason it works again, but I'm sure what I have changed.