private static void OnCollectionChanged([NotNull, ItemCanBeNull] ObservableWrappedCollection <TSource, TTarget> self, [NotNull] object sender, [NotNull] NotifyCollectionChangedEventArgs e)
        {
            Contract.Requires(self != null);
            Contract.Requires(sender != null);
            Contract.Requires(e != null);

            self.SourceItems_CollectionChanged(sender, e);
        }
 private static void OnCollectionChanged([NotNull, ItemCanBeNull] ObservableWrappedCollection <TSource, TTarget> self, [NotNull] object sender, [NotNull] NotifyCollectionChangedEventArgs e)
 {
     self.SourceItems_CollectionChanged(sender, e);
 }