来自xCode 6的iOS Master-Detail应用程序模板无法在iOS 7上运行

我正在尝试从xCode 6模板开发一个主 - 细节iOS应用程序(仅限iPad).iOS 8运行良好,但在iOS 7.0或7.1上运行会在运行时发生崩溃,我评论过:

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    // Override point for customization after application launch.
    UISplitViewController *splitViewController = (UISplitViewController *)self.window.rootViewController;
    UINavigationController *navigationController = [splitViewController.viewControllers lastObject];

    // this line throws a "[MasterViewController topViewController]: unrecognized selector sent to instance 0x796dde90"
    navigationController.topViewController.navigationItem.leftBarButtonItem = splitViewController.displayModeButtonItem;
    splitViewController.delegate = self;
    return YES;
}