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) {
        if (l1==null&&l2==null) {
            return null;
        }

        ListNode previous = new ListNode(0);
        ListNode head = previous;

        while (l1!=null||l2!=null) {
            if (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;
            //l1 and l2 have different length
            } else {
                if (l1!=null) {
                    head.next = l1;
                } else {
                    head.next = l2;
                }
                break;
            }
        }
        return previous.next;

    }