Double a Number Represented as a Linked List

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

class Solution:
    def doubleIt(self, head: Optional[ListNode]) -> Optional[ListNode]:
        if head.val > 4:
            head = ListNode(0, head)
        node = head
        while node:
            node.val = (node.val * 2) % 10
            if node.next and node.next.val > 4:
                node.val += 1
            node = node.next
        return head