documentcloud/underscore — pull request #651 by benjamn (2012-06-22 20:14:34+00:00)
Title: Make _.each skip holes in sparse arrays

Most immediately, this change is required to match the behavior of the
native forEach method.

The changes to _.isEmpty are required to fulfill the promises of this
comment: "An 'empty' object has no enumerable own-properties."

In general, wherever we bother to skip non-own object properties using
_.has, we should be careful to skip array holes as well.