yiisoft/yii — pull request #2789 by Corfiot (2013-08-19 10:15:03+00:00)
Title: Fixes #2787 by treating null returned by a formatter as a null attribute

Formatters may need to be transparent to output. Returning null would allow a formatter to "get out of the way" of the rending pipeline, either by design or by failing silently. #2787