symfony/symfony-docs — pull request #1702 by ardianys (2012-09-12 07:40:36+00:00)
Title: Update cookbook/form/data_transformers.rst

Hi,

I have followed this cookbook and got this error

```bash
The option "em" does not exist. Known options are: "attr", ..., "widget_type"
```

It tooks me some hour to get this work.

You should provide ```'em'``` in ```setDefaultOptions``` to avoid this error.

Thanks