Made use of `EMPTY_VALUES` in `ModelChoiceField.clean()`.
Made use of `EMPTY_VALUES` in `ModelChoiceField.clean()`.

--HG--
extra : convert_revision : svn%3Abcc190cf-cafb-0310-a4f2-bffc1f526a37/django/trunk%406699

adieu/django-nonrel,adieu/django-nonrel,adieu/django-nonrel