比较数据类型，为什么测试没有看到None？

如何解决比较数据类型，为什么测试没有看到None？

我有这个函数来检查输入数据结构是否有正确的字段。

def validate_response(RequiredTypes: RawCustomResponseDataStruct,ResultToCheck: RawCustomResponseData) -> bool:
if isinstance(RequiredTypes,dict) and isinstance(ResultToCheck,dict):
    return all(k in ResultToCheck and validate_response(RequiredTypes[k],ResultToCheck[k]) for k in RequiredTypes)
if isinstance(RequiredTypes,list) and isinstance(ResultToCheck,list):
    return all(validate_response(RequiredTypes[0],c) for c in ResultToCheck)
if isinstance(RequiredTypes,type):
    return isinstance(ResultToCheck,RequiredTypes)
return False

类及其字段如下所示：（我制作了字典副本，以便可以使用 isinstance，因为我不想导入更多库）。

class Crawler(TypedDict):
is_crawler: bool
category: Union[str,None]
last_seen: Union[str,None]

CrawlerStruct = {
    "is_crawler": bool,"category": Union[str,None],"last_seen": Union[str,None]}

当我使用以下输入运行此测试时：

def test_validate_response():
ResultToCheck = {"ua": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_14_0) AppleWebKit/537.36 (KHTML,like Gecko) Chrome/71.0.3578.98 Safari/537.36 isBot3","type": "browser","brand": "Apple","name": "Mac","url": "https://about.google/","os": {"name": "macOS 10.14 Mojave","code": "macos_10_14","url": "https://en.wikipedia.org/wiki/MacOS_Mojave","family": "macOS","family_code": "macos","family_vendor": "Apple Inc.","icon": "https://assets.userstack.com/icon/os/macosx.png","icon_large": "https://assets.userstack.com/icon/os/macosx_big.png"},"device": {"is_mobile_device": False,"type": "desktop","brand_code": "apple","brand_url": "https://www.apple.com/","name": "Mac"},"browser": {"name": "Chrome","version": "71.0.3578.98","version_major": "71","engine": "WebKit/Blink"},"crawler": {"is_crawler": False,"category": None,"last_seen": None}}
result = validate_response(RawCustomResponseDataStruct,user_agent)
assert result is True

失败了。

但是，如果我删除联合，并且只对类和字典使用 str 并运行测试，将“爬虫”对象更改为具有以下值

"crawler": {"is_crawler": False,"category": "None","last_seen": "None"}

通过了。为什么是这样？为什么不识别 None 类型？