symfony/symfony — pull request #6178 by Tobion (2012-12-03 18:37:27+00:00)
Title: [Validator] made ExecutionContext more consistent

The default should be an empty string instead of null because
1. a string is expected according to phpdoc
2. its more consistent with `validate($value, $groups = null, $subPath = '', $traverse = false, $deep = false)` and `validateValue($value, $constraints, $groups = null, $subPath = '')` that both have `''` as default for subPath