When checking your class you will find that iOS7 returns a different type.
Review the logic for which you need the check. You should not have to use introspection to react appropriately to a people picker action. Just implement the standard delegate method from ABPeoplePickerNavigationControllerDelegate. In particular, you have to implement:
- (BOOL)peoplePickerNavigationController:
(ABPeoplePickerNavigationController *)peoplePicker
shouldContinueAfterSelectingPerson:(ABRecordRef)person;