Observer with Null Object Pattern

Observer.cs

internal class Observer<T> : IObserver<T>
{
    static Action<Exception> onError = ((e) => { });
    static Action onCompleted = (() => { });

    private readonly Action<T> _onNext;
    private readonly Action<Exception> _onError;
    private readonly Action _onCompleted;

    public Observer(
    Action<T> onNext,
    Action<Exception>? onError = null,
    Action? onCompleted = null
        )
    {
        _onNext = onNext;
        _onError = onError ?? Observer<T>.onError;
        _onCompleted = onCompleted ?? Observer<T>.onCompleted;
    }


    public void OnCompleted() => _onCompleted();
    public void OnError(Exception error) => _onError(error);
    public void OnNext(T value) => _onNext(value);
}