minor tweaks - #173

'RoomsPage.PropertyChanged' hides inherited member 'AvaloniaObject.PropertyChanged'. Use the new keyword if hiding was intended.

'RoomDetailsPage.PropertyChanged' hides inherited member 'AvaloniaObject.PropertyChanged'. Use the new keyword if hiding was intended.

'PopupWindow.PropertyChanged' hides inherited member 'AvaloniaObject.PropertyChanged'. Use the new keyword if hiding was intended.

'FriendsPage.PropertyChanged' hides inherited member 'AvaloniaObject.PropertyChanged'. Use the new keyword if hiding was intended.

Nullability of reference types in type of parameter 'parameter' of 'object NullToBoolConverter.ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)' doesn't match implicitly implemented member 'object? IValueConverter.ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'value' of 'object NullToBoolConverter.ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)' doesn't match implicitly implemented member 'object? IValueConverter.ConvertBack(object? value, Type targetType, object? parameter, CultureInfo culture)' (possibly because of nullability attributes).

Nullability of reference types in type of parameter 'parameter' of 'object NullToBoolConverter.Convert(object? value, Type targetType, object parameter, CultureInfo culture)' doesn't match implicitly implemented member 'object? IValueConverter.Convert(object? value, Type targetType, object? parameter, CultureInfo culture)' (possibly because of nullability attributes).

Cannot convert null literal to non-nullable reference type.

Cannot convert null literal to non-nullable reference type.