Should `None` be an acceptable `default_section` parameter of `configparser.ConfigParser`

Since this is typing related, I'll ask here before adding to cpython's 5k+ issues.

In https://github.com/pypa/setuptools/pull/4604#discussion_r1777834900 (read this comment for more details) , I found a usage of configparser.ConfigParser(default_section=None, delimiters=("=",)) seemingly to not have a default section.

The documentation doesn't make any mention of leveraging that behaviour. So we're left wondering if the parameter type should be updated (along as a request for cpython's doc to make it explicit), use "" instead, or just type-ignoring it, marking as using undocumented behaviour.

Start by reviewing the ConfigParser default_section annotation in the relevant typeshed stub and the linked setuptools discussion, then compare it with the documented and observed behavior. Done means resolving whether None is supported and updating the type or documenting the behavior accordingly.