.NET: Merge statement for lists

MergeExtensions.cs

public static void Merge<T>(this IEnumerable<T> from, IEnumerable<T> into,
    Action<T> newItem = null, Action<T> existingItem = null, Action<T> removedItem = null,
    IEqualityComparer<T> comparer = null)
{
    if (newItem != null)
    {
        var newItems = from.Except(into, comparer).ToList();

        foreach (var item in newItems)
        {
            newItem(item);
        }
    }

    if (existingItem != null)
    {
        var existingItems = from.Intersect(into, comparer).ToList();

        foreach (var item in existingItems)
        {
            existingItem(item);
        }
    }

    if (removedItem != null)
    {
        var removedItems = into.Except(from, comparer).ToList();

        foreach (var item in removedItems)
        {
            removedItem(item);
        }
    }
}