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.

public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode dummy = new ListNode(-1);
        ListNode head = dummy;

        while (l1 != null && l2 != null) {
            if (l1.val < l2.val) {
                head.next = l1;
                l1 = l1.next;
            } else {
                head.next = l2;
                l2 = l2.next;
            }
            head = head.next;
        }

        if (l1 != null) {
            head.next = l1;
        }

        if (l2 != null) {
            head.next = l2;
        }

        return dummy.next;
    }