mapBy('parent') yields the Window object for nulls

[macu]

I have a function that recurses up a tree from a source array of leaf nodes, collecting parents along the way via nodes.mapBy('parent'). Normally, node.get('parent') yields undefined, but suppose it ever yields null. On the next pass over the array, to get the parents of the parents, my function fell into an infinite loop which led me to discover that mapBy yields the Window object for nulls, and window.parent refers back to window. Nice!

http://jsbin.com/fehayaza/43/

[rwjblue]

Ember.get(null, 'parent') //=> Window

See #3852 for more details (and the fix).