Switching to ios 9 sdk gives exc_bad_access

Question

My program works fine before installing xcode 7 and switches to ios 9.

now one of my views gives exc_bad_access (Code = 2, ...) :

turning on zombie mode and using the tool did not help, and debugging still shows the above errors without any useful description.

after adding some nslog and breakpoint i recognize "pushViewController" gives

mistake:

UIStoryboard *storyboard;
if (UI_USER_INTERFACE_IDIOM() == UIUserInterfaceIdiomPad) {
storyboard = [UIStoryboard storyboardWithName:@"Ipad" bundle:nil];   
        }
       else
        {
storyboard = [UIStoryboard storyboardWithName:@"Iphone" bundle:nil];
         }
AtestViewController *atvc = [storyboard instantiateViewControllerWithIdentifier:@"AVC"];

[self.navigationController pushViewController:atvc animated:YES];

nothing has changed in the code until i swtich to xcode 7 and ios 9 !!

as well as my other pushViewController in the program works well and

The encoding method is the same as above.