When you render a partial with a collection, rendering silently fails
if the collection object doesn't respond to #to_ary. This means that a
class that mixes in Enumerable won't work, unless you also add a
to_ary method. A couple of issues of thoughts regarding this:
1) Failing silently is probably not the best thing to do, especially
since this behavior isn't documented anywhere.
2) Is relying on solely on #to_ary the best idea? Seems that any
object that responds to #to_a should be usable as well?