facebook/react — pull request #1378 by sstur (2014-04-08 21:15:28+00:00)
Title: Use default prop when prop specified is `null` *or* `undefined`

The undesired behavior can be seen here:
http://jsfiddle.net/sstur/kb3gN/1760/

This commits patches React to treat `null` and `undefined` more similarly in the case of default props.