ZoomKamera_Starter launches to black screen, Error: (null)

[slgraff]

After completing the code changes to ZoomKamera_Starter from Listing 7.2 and running the resulting app I find that the app will build, then run on my iPhone 6 but only displays a black screen. A few seconds later Xcode will display the error 'ZoomKamera [356:21199] Error: (null)' I reviewed the code I entered to ensure that it was accurate. Various troubleshooting measures (cleaning project, deleted app on iPhone, restarting iPhone, restarting Xcode) did not resolve issue. It's also reproducible when running project in second user account on Mac. Also occurs when running ZoomKamera_Starter without making any changes.

ZoomKamera_Final runs fine however.

This is on a MacBook Pro (mid-2012) running OS X 10.12.1 Sierra and Xcode 8.1 (8T61a).

[slgraff]

Of further note, after completing the remainder of the Video Zooming section of Chapter 7 the app now builds and run fine. I haven't yet chased down the cause.