Property-based dependency injection in view controller with one if statement

ViewControllerPropertyBasedDependencyInjectionOneIfStatement.swift

class ViewController: UIViewController {
    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if segue.identifier == PhotoDetailViewControllerIdentifier,
            let viewController = segue.destinationViewController as? PhotoDetailViewController {
                viewController.photo = Photo()
        }
    }
}