Run UIViewController inside UINavigationController as a second view of UISplitViewController

Run UIViewController inside UINavigationController as a second view of
UISplitViewController

I have a problem trying to access a navigation controller of the view
controller from it, always returns as nill to me, though it is shown
within the navigation controller. Here is what I have (I have a split view
controller, that is presented as tab controller for master and
viewcontroller (inside navigation controller) as detail):
FirstDetailViewController *fdvc = [[FirstDetailViewController alloc]
initWithNibName:@"FirstDetailViewController" bundle:nil];
UINavigationController *fdvcNav = [[UINavigationController alloc]
initWithRootViewController:fdvc];
NSArray *ipadVCs = [[NSArray alloc] initWithObjects:tabController,
fdvcNav, nil];
UISplitViewController *splitvc = [[UISplitViewController alloc]
initWithNibName:nil bundle:nil];
[splitvc setViewControllers:ipadVCs];
[[splitvc view] setBackgroundColor:[UIColor colorWithPatternImage:[UIImage
imageNamed:@"splitViewControllerBG"]]];
[splitvc setDelegate:fdvc];
[[self window] setRootViewController:splitvc];
[[self window] makeKeyAndVisible];
But when I'm trying to access a navigation controller from the fdvc view
controller in ViewDidLoad with [self navigationController] it gives me
(Null) always. Thanks!