[Refactor] fix ruff rule B039: mutable-contextvar-default

[LeoLiao123]

Why are these changes needed?

Replace mutable default value with None to prevent shared state across ContextVar.get() calls

ref : https://docs.astral.sh/ruff/rules/mutable-contextvar-default/

Related issue number

#47991

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[LeoLiao123]

@MortalHappiness PTAL

[MortalHappiness]

It's better to follow the reference and check it with if current_request_context is None, as None is not the only value with a False boolean value in Python.

[LeoLiao123]

Thanks for the suggestion. Updated to check with is None .

[MortalHappiness]

Still need to update other files that use this variable. You can create an utility function like

def get_serve_request_context():
    if _serve_request_context.get() is None:
        _serve_request_context.set(_RequestContext())
    return serve_request_context.get()

[LeoLiao123]

I've updated all related files and implemented the utility function for get_serve_request_context().

[aslonnie]

@zcin @edoakes could you help review & approve?

[edoakes]

Looks great pending my one comment -- thanks for the fix!

[edoakes]

Suggested change

	@DeveloperAPI
	def get_serve_request_context():
	def _get_serve_request_context():

this is an internal API, not public at the moment

[LeoLiao123]

Fixed, thanks for the review.