Which XXX completes the append() method in the Java LinkedList class for a doubly-linked list? public void append (Node newNode) { if (m_head == null) { m_head = newNode; m_tail = newNode; } } else { } m_tail.next = XXX m_tail = newNode; newNode.previous = m_tail; m_head = newNode; newNode; m_head.next newNode.previous = m_head; = newNode;