Nullability of reference types in type of 'event PropertyChangedEventHandler SubscriptionBase.PropertyChanged' doesn't match implicitly implemented member 'event PropertyChangedEventHandler? INotifyPropertyChanged.PropertyChanged'.

Nullability of reference types in type of parameter 'propertyName' of 'IEnumerable SubscriptionBase.GetErrors(string propertyName)' doesn't match implicitly implemented member 'IEnumerable INotifyDataErrorInfo.GetErrors(string? propertyName)' (possibly because of nullability attributes).

The result of the expression is always 'false' since a value of type 'Guid' is never equal to 'null' of type 'Guid?'

Thrown value may be null.

Nullability of reference types in type of parameter 'sender' of 'void SubscriptionBase.OnPropertyChanged(object sender, PropertyChangedEventArgs e)' doesn't match the target delegate 'PropertyChangedEventHandler' (possibly because of nullability attributes).

Dereference of a possibly null reference.

Possible null reference argument for parameter 'path' in 'DirectoryInfo Directory.CreateDirectory(string path)'.

Dereference of a possibly null reference.

Possible null reference argument for parameter 'path' in 'DirectoryInfo Directory.CreateDirectory(string path)'.