Null check operator used on a null value

[d9media]

Hi guys,

I recently investigated an issue where our app would get stuck at splashscreen for some users. I'm now convinced I can reproduce the issue.

When you enable "use network-provided time zone" in Android (settings > system > date&time) , initialization of TimeMachine fails with the following stacktrace:

I/flutter (26553): ----------------FIREBASE CRASHLYTICS----------------
I/flutter (26553): Null check operator used on a null value
I/flutter (26553):
I/flutter (26553): #0      TimeMachine.initialize
package:time_machine/…/platforms/vm.dart:95
I/flutter (26553): <asynchronous suspension>
I/flutter (26553): #1      main.<anonymous closure>
package:***/main.dart:115
I/flutter (26553): <asynchronous suspension>
I/flutter (26553): #2      main
package:***/main.dart:110
I/flutter (26553): <asynchronous suspension>

pointing to vm.dart:93 ff.:

   var local = timeZoneOverride != null ? await tzdb.getZoneOrNull(timeZoneOverride) : await _figureOutTimeZone(tzdb);
    // todo: cache local more directly? (this is indirect caching)
    TzdbIndex.localId = local!.id;   // <-- baaang

When you set a location instead, everything works. I can't say whether this is an issue for iOS too but we did have user reports with a similar crash pattern.

It looks local can be null when network-provided time fails or timezone is set to GMT. In that case, we can't use null operator.

I don't really know TimeMachine well enough yet to suggest a solution but I still wanted to bring this your attention.

[rich-j]

We've hit this with Android Play store testing where some of the test devices have uncommon/undefined time zone names. I don't know if TimeMachine could provide a reasonable fallback default. We have implemented our own fallback to UTC (which is always defined) when the initialize throws an exception:

FlutterTimezone.getLocalTimezone()
  .then((timeZone) => TimeMachine.initialize({"rootBundle": kIsWeb ? null : rootBundle, "timeZone": timeZone}))
  .catchError((_) => TimeMachine.initialize({"rootBundle": kIsWeb ? null : rootBundle, "timeZone": "UTC"}));

[tigloo]

I fixed the issue in the fork here: https://pub.dev/packages/time_machine2