Non-nullable field 'data' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the field as nullable.

Converting null literal or possible null value to non-nullable type.

Possible null reference argument for parameter 'apiKey' in 'User AuthProvider.GetUser(string apiKey)'.

Dereference of a possibly null reference.

Nullability of reference types in type of parameter 'source' of 'void NotificationSystem.OnTimedEvent(object source, ElapsedEventArgs e)' doesn't match the target delegate 'ElapsedEventHandler' (possibly because of nullability attributes).

Possible null reference return.

Converting null literal or possible null value to non-nullable type.

Non-nullable field '_timer' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the field as nullable.

Possible null reference assignment.