knockout/knockout — pull request #1200 by timtucker (2013-11-11 20:39:11+00:00)
Title: Check for existance of array instead of reassigning

Seems to be somewhat faster for null / undefined values: http://jsperf.com/exists-vs-reassignment

Also applied the same method to arrayForEach, arrayIndexOf, arrayFirst so that null / undefined inputs don't result in errors.