emberjs/ember.js — pull request #1251 by sly7-7 (2012-08-09 10:09:23+00:00)
Title: initialize the content of ArrayController if not defined

Answering this question: http://stackoverflow.com/questions/11829626/ember-js-pushobject-not-pushing, it seems that users feel puzzled with the fact that the ArrayController content is null, and must define it at creation time.