facebook/react — pull request #1958 by chenglou (2014-07-30 00:48:13+00:00)
Title: [Addons] Fix TransitionGroup null children bug

Fixes #1949

When we render two children to two nulls, `ReactTransitionChildMapping.getChildMapping` now returns `{}` rather than `{'.0': ..., '.1': ...}`. Otherwise mergeChildMapping doesn't doesn't understand that the children have disappeared.