If invalid value submitted the select choice throws an exception TransformationFailedException where radio\checkbox choices set the value to NULL.
This behavior cause some problems at validation stage.
- First one is
Choice constraint. It do nothing for NULL values.
- Next problem more serious. If you dont have
NotBlank constraint at the field you will pass validation with NULL value where someone would expect a value from choice set.
Personally I prefer TransformationFailedException for such cases.