emberjs/ember.js — pull request #2015 by twinturbo (2013-02-08 13:02:18+00:00)
Title: Guard against render(undefined)

render(undefined) was doing absolutely horrible things. I found this
problem because I passed an undefined variable as the first argument.
This ended up changing containers on controllers and doing other
absolutely horrible things.

I don't even know how the consequences happened, but they took forever to debug and it was absolute hell.