Lazy chains errors

gistfile1.txt

Uncaught TypeError: Cannot call method 'didChange' of undefined ember.js?body=1:2373
chainsDidChange ember.js?body=1:2373
Ember.propertyDidChange ember.js?body=1:2307
Ember.EachProxy.Ember.Object.extend.contentKeyDidChange ember.js?body=1:13319
sendEvent ember.js?body=1:2106
notifyObservers ember.js?body=1:2441
Ember.propertyDidChange ember.js?body=1:2308
iterDeps ember.js?body=1:2345
dependentKeysDidChange ember.js?body=1:2329
Ember.propertyDidChange ember.js?body=1:2306
ChainNodePrototype.chainDidChange ember.js?body=1:3492
ChainNodePrototype.chainDidChange ember.js?body=1:3490
ChainNodePrototype.chainDidChange ember.js?body=1:3490
ChainNodePrototype.chainDidChange ember.js?body=1:3490
ChainNodePrototype.didChange ember.js?body=1:3527
chainsDidChange ember.js?body=1:2373
Ember.propertyDidChange ember.js?body=1:2307
Ember.EachProxy.Ember.Object.extend.contentKeyDidChange ember.js?body=1:13319
sendEvent ember.js?body=1:2106
ObserverSet.flush ember.js?body=1:2222
Ember.endPropertyChanges ember.js?body=1:2396
DeferredActionQueues.flush ember.js?body=1:4749
Backburner.end ember.js?body=1:4826
Backburner.run ember.js?body=1:4865
Ember.run ember.js?body=1:5196
Ember.EventDispatcher.Ember.Object.extend._bubbleEvent ember.js?body=1:15527
(anonymous function) ember.js?body=1:15471
Ember.handleErrors ember.js?body=1:446
(anonymous function) ember.js?body=1:15462
jQuery.event.dispatch jquery.js?body=1:4619
elemData.handle