App crash on launch

[Allansk2]

2017-02-21 11:33:38.864 PDTSimpleCalendarTestsHostApp[3554:109359] *** Assertion failure in -[UIApplication _runWithMainScene:transitionContext:completion:], /BuildRoot/Library/Caches/com.apple.xbs/Sources/UIKit_Sim/UIKit-3600.6.21/UIApplication.m:3680
2017-02-21 11:33:38.867 PDTSimpleCalendarTestsHostApp[3554:109359] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Application windows are expected to have a root view controller at the end of application launch'