Bug Report for serialize-and-deserialize-binary-tree

[DezzardHD]

Bug Report for https://neetcode.io/problems/serialize-and-deserialize-binary-tree

Please describe the bug below and include any steps to reproduce the bug or screenshots if possible.
The following test case fails on leetcode but not on neetcode: [4,-7,-3,null,null,-9,-3,9,-7,-4,null,6,null,-6,-6,null,null,0,6,5,null,9,null,null,-1,-4,null,null,null,-2]

Broken code:

class Codec:
    
    # Encodes a tree to a single string.
    def serialize(self, root: Optional[TreeNode]) -> str:
        # preorder traversal
        res = ""
        def preorder(node):        
            nonlocal res
            if not node:
                res = res + "#"
                return
            res = res + "#" + str(node.val)
            preorder(node.left)
            preorder(node.right)
            return
        preorder(root)
        return res

    # Decodes your encoded data to tree.
    def deserialize(self, data: str) -> Optional[TreeNode]:
        arr = [None if not x else int(x) for x in data.split("#")]
        print(arr)
        def preorder_build(idx: int) -> (Optional[TreeNode], int):
            nonlocal arr
            if len(arr) <= idx or not arr[idx]:
                return None, idx + 1
            node = TreeNode(arr[idx])
            idx += 1
            node.left, idx = preorder_build(idx)
            node.right, idx = preorder_build(idx)
            return node, idx
        root, idx = preorder_build(1)
        return root

The test case includes a node value equal to zero.
My deserializer checked for not arr[idx] which is true for None and zero.
I intended to only check for None vaues.

Solution: Add the test case mentioned above to the test case collection of the question.