Nullability of reference types in type of parameter 'sender' of 'void Player.OnPlaybackFinished(object sender, EventArgs e)' doesn't match the target delegate 'EventHandler' (possibly because of nullability attributes).

Non-nullable event 'PlaybackFinished' must contain a non-null value when exiting constructor. Consider declaring the event as nullable.

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

Cannot convert null literal to non-nullable reference type.

Non-nullable field 'playbackTimer' must contain a non-null value when exiting constructor. Consider declaring the field as nullable.

Non-nullable field 'playStopwatch' must contain a non-null value when exiting constructor. Consider declaring the field as nullable.

Non-nullable field 'fileName' must contain a non-null value when exiting constructor. Consider declaring the field as nullable.

Non-nullable event 'PlaybackFinished' must contain a non-null value when exiting constructor. Consider declaring the event as nullable.

Nullability of reference types in type of parameter 'sender' of 'void UnixPlayerBase.HandlePlaybackFinished(object sender, EventArgs e)' doesn't match the target delegate 'EventHandler' (possibly because of nullability attributes).