C# Double linked list swapping

public DoubleLink SwapLinkWithNext(DoubleLink link)
        {
            DoubleLink next = link.Next;
            if (next == null)
            {
                return null;
            }
            DoubleLink previous = link.Previous;
            DoubleLink current = link;
            DoubleLink nextNext = next.Next;

            current.Next = nextNext;
            current.Previous = next;

            next.Previous = previous;
            next.Next = current;

            if (previous == null)
            {
                First = next;
            } else {
                previous.Next = next;
            }
            if (nextNext == null)
            {
                Last = current;
            } else {
                nextNext.Previous = current;
            }

            return next;
        }

public void BubbleSort()
        {
            DoubleLink lastEnd = new DoubleLink();
            while (lastEnd != null)
            {
                Boolean swapped = false;
                DoubleLink link = First;
                while (link !=null){
                    if (link == Last || link == lastEnd)
                    {
                        lastEnd = link;
                        break;
                    }
                    if (link.Naw.CompareTo(link.Next.Naw) == 1)
                    {
                        SwapLinkWithNext(link);
                        swapped = true;
                    }
                    link = link.Next;
                }
                if (swapped == false )
                {
                    break;
                }
            }
        }