'Check that `radio_fields` is a dictionary.'

def _check_radio_fields(self, obj):

    if (not isinstance(obj.radio_fields, dict)):
        return must_be('a    dictionary', option='radio_fields', obj=obj, id='admin.E021')
    else:
        return list(chain.from_iterable(((self._check_radio_fields_key(obj, obj.model, field_name, 'radio_fields') + self._check_radio_fields_value(obj, val, ('radio_fields["%s"]' % field_name))) for (field_name, val) in obj.radio_fields.items())))
