I’m attempting this leetcode question.

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def addTwoNumbers(self, l1: Optional[ListNode], l2: Optional[ListNode]) -> Optional[ListNode]:
        num1 = []
        n1 = l1
        while n1.next:
            num1.append(n1.val)
            n1 = n1.next
        
        n2 = l2
        num2 = []
        while n2.next:
            num2.append(n2.val)
            n2 = n2.next
        
        num1 = ''.join([str(x) for x in num1][::-1])
        num2 = ''.join([str(x) for x in num2][::-1])

        num1 = int(num1)
        num2 = int(num2)

When I run the code, I get this error

ValueError: invalid literal for int() with base 10: ''
           ^^^^^^^^^
    num1 = int(num1)
Line 23 in addTwoNumbers (Solution.py)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ret = Solution().addTwoNumbers(param_1, param_2)
Line 50 in _driver (Solution.py)
    _driver()
Line 61 in <module> (Solution.py)

As far as I can tell, this shouldn’t be happening, as these seem to be valid literals.

I’ve also tried converting to float first and then int, via

num1 = int(float(num1))
        num2 = int(float(num2))

which gives this error

ValueError: could not convert string to float: ''
               ^^^^^^^^^^^
    num1 = int(float(num1))
Line 23 in addTwoNumbers (Solution.py)
          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    ret = Solution().addTwoNumbers(param_1, param_2)
Line 50 in _driver (Solution.py)
    _driver()
Line 61 in <module> (Solution.py)

What am I missing?