Merge Two Sorted Linked Lists

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */

class Solution {
    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {
        ListNode dummy = new ListNode(0);
        ListNode node = dummy;

        while(list1 != null && list2 != null) {
            if(list1.val < list2.val){
                node.next = list1;
                list1 = list1.next;
            } else {
                node.next = list2;
                list2 = list2.next;
            }

            node = node = node.next;
        }

        if(list1 != null) node.next = list1;
        else node.next = list2;

        return dummy.next;
    }
}

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next

class Solution:
    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
        if list1 is None:
            return list2
        if list2 is None:
            return list1
        
        if list1.val <= list2.val:
            list1.next = self.mergeTwoLists(list1.next, list2)

            return list1
        else:
            list2.next = self.mergeTwoLists(list1, list2.next)

            return list2