private static void OnPersonUnavailable(object?sender, ItemUnavailableEvent <Person> e)
 {
     System.Console.WriteLine($"OnPersonUnavailable: {e.UnavailableEntity.Entity}");
 }
 protected virtual void OnItemUnavailable(ItemUnavailableEvent <TEntity> e)
 {
     ItemUnavailable?.Invoke(this, e);
 }