从链表的末尾返回第N个节点

我正在尝试从链接列表的末尾返回第N个节点，但是遇到错误。所以这就是我到目前为止所得到的：

class Node {
    int data;
    Node next;

    public Node(int data) {
       this.data = data;
       this.next = null;
    }
}

public class LinkedList {
    Node head;
    Node tail;

    public LinkedList() {
        head = tail = null;
    }

    public boolean isEmpty(){
        return head==null;
    }

    public void insertFirst(int data) {
        Node newLink = new Node(data);

        if (head == null) {// list is empty
            tail = newLink;
        }

        newLink.next = head; 
        head = newLink ; 
    }

    public Node nthFromLast(Node node, int n){
        for (int i = 0; i < n; i++) {
            if (head == null) {
                return null;
            }
            tail = tail.next;
        }
        while (head.next != null) {
            head = head.next;
            tail = tail.next;
        }
        return tail;
    }

    public static void main(String[] args) {
        LinkedList list = new LinkedList();
        Node node = new Node(4);
        list.insertFirst(16);
        list.insertFirst(23);
        list.insertFirst(55);
        list.nthFromLast(node, 3);
    }

}

I'm getting a NullPointerException for some reason and I can't figure it out. I'd love for someone to point out my error in the code so I could understand the subject better.