emberjs/ember.js — pull request #9914 by mixonic (2014-12-14 16:50:17+00:00)
Title: [BUGFIX beta] Do not stringify null classes, allow unquoted bind-attr class

Fixes #9893 and #9890.

@mmun as discussed in #9908 I've added a concat helper to the stream utils that takes an argument for join value. Additionally I've added a `chainStream` helper that either processes immediately or chains a stream onto the passed value. This decreases the crazy in class name bindings.