GetCalendarsAsync on Android throws null exception

[steffos]

Thanks for a great plugin! Occasionally I'm seeing the following crash stack trace in my app log when calling GetCalendarsAsync on Android:

Xamarin Exception Stack:
System.NullReferenceException: Object reference not set to an instance of an object
  at Plugin.Calendars.CalendarsImplementation.IterateCursor[T] (Android.Database.ICursor cursor, System.Func`1[TResult] func) <0x7504be4200 + 0x00160> in <66a7b4e231214800b78812276a0f1b58>:0
  at Plugin.Calendars.CalendarsImplementation+<>c.<GetCalendarsAsync>b__13_0 () <0x7504bdd894 + 0x000d3> in <66a7b4e231214800b78812276a0f1b58>:0

Just had a look at the implementation of GetCalendarsAsync for Android:

Calendars/Calendars/Calendars.Plugin.Android/CalendarsImplementation.cs

Lines 79 to 86 in d059b7b

	public Task<IList<Calendar>> GetCalendarsAsync() => Task.Run(() =>
	{
	var cursor = Query(_calendarsUri, _calendarsProjection);
	var calendars = IterateCursor(cursor, () => GetCalendar(cursor));
	return calendars;
	});

It seems that on some devices when certain conditions are met the cursor query on line 81 returns null. At least that's how I interpret the stack trace.

Im thinking a null check on the cursor variable might fix this?

[TheAlmightyBob]

Thanks for the report and investigation! Are you using the latest version, 1.1.0?

One of the changes between 1.0.0 and 1.1.0 is that there is now a null check in Query, so it shouldn't be possible for it to return null (it would instead itself throw a NullReferenceException, but a more specific one).

If you're getting this with 1.1.0, then I'm not sure what it could be... In general, the move to Nullable type support means that there really shouldn't be any unexpected NullReferenceExceptions...