Leetcode || Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

package pack;

class ListNode {
    int val;
    ListNode next;
    ListNode(int x) { val = x; }
}

class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {

        if(l1 == null) 
            return l2;
        if(l2 == null)