在二进制搜索树中获取None作为额外输出，而不是仅获取最小值

class TreeNode:
    def __init__(self, val=0, left=None, right=None):
        self.val = val
        self.left = left
        self.right = right

def get_none_in_bst(root):
    result = []
    inorder_traversal(root, result)
    return result

def inorder_traversal(node, result):
    if node:
        inorder_traversal(node.left, result)
        if node.val is None:
            result.append(node.val)
        inorder_traversal(node.right, result)

# 示例用法
# 创建一个BST
root = TreeNode(5)
root.left = TreeNode(3)
root.right = TreeNode(7)
root.left.left = TreeNode(2)
root.left.right = TreeNode(None)
root.right.left = TreeNode(6)
root.right.right = TreeNode(8)

# 获取None作为额外输出
output = get_none_in_bst(root)
print(output)  # 输出: [None]