Add two numbers problem linked list

Add two numbers in a given linked lists

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order, and each of their nodes contains a single digit. Add the two numbers and return the sum as a linked list. You may assume the two numbers do not contain any leading zero, except the number 0 itself.

    private Node addTwoNumbers(Node n, Node m, int carry) {
        //we have to start from reverse linked list then move to front so its recursion
        if(n == null && m == null && carry == 0) {
            return null;
        }
        int val1 = (n !=null) ? n.val : 0;
        int val2 = (m !=null) ? m.val : 0;
        int cal = val1 + val2 + carry;

        Node nNode = new Node(cal%10, null);
        nNode.next = addTwoNumbers(n.next, m.next, cal/10);
        //Last node is the node with 
        return nNode;
    }

 private class Node {
        Node next ;
        int val ;
        Node(int v, Node n){
            this.next = n;
            this.val = v;
        }
    }