macOS app error and then stuck

Hi,

Downloaded the macOS app (on an MBP 13", early 2015, macOS 10.12.1), ran it, entered my email and password and was asked to create a name for my device. When I set it, the app briefly showed an error top bar saying something like "can't read the property stringValue of null" (didn't quite have time to read it). The app is now stuck on the screen where I set my device name, even if I restart it. Clicking Continue or Back seemingly does nothing at all.

I did, however, get an email about having created a desktop or laptop device, and of having created a "paper key". I did no such thing.

Reproduce the onboarding flow on the reported early-2015 MacBook Pro running macOS 10.12.1, starting after login at the device-name screen. Investigate the error mentioning stringValue of null and the nonresponsive Continue and Back controls; done means onboarding can proceed or go back without the unexpected device and paper-key creation.

Written by the indexing model from the issue text.