c# revert a LinkedList

void ReverseLinkedList(LinkedList ls)
{
    if ( ls == null || ls.Head == null )
        return;
    ListNode head = ls.Head;
    ListNode current = head.Next;
    while(current!=null)
    {
        ListNode tmp = current;
        current = current.Next;
        tmp.Next = head;
        head = tmp;
    }
    ls.Head.Next = null;
    ls.Head = head;
}