ReactiveCocoa/ReactiveCocoa — pull request #1203 by calebd (2014-03-27 07:27:14+00:00)
Title: Return nil if count is 0.

This fixes an issue where `RACIndexSetSequence` would return data from `self.indexes` in `head` even if it represented an empty index set. `head` now returns `nil` if it represents an empty set.