Fix AttributeError in Session.prepare_request() when Request.method is None

[tboy1337]

Summary

This PR fixes a bug where Session.prepare_request() would raise an AttributeError when called with a Request object that has method=None.

Problem

When creating a Request object without specifying a method (e.g., Request(url="https://example.com/")), the method attribute defaults to None. Subsequently calling Session.prepare_request() with this request would crash because the code attempted to call .upper() on None:

# Before fix
p.prepare(
    method=request.method.upper(),  # AttributeError: 'NoneType' object has no attribute 'upper'
    ...
)

Solution

Changed the code to default to "GET" when the method is None, matching standard HTTP behavior:

# After fix
p.prepare(
    method=(request.method or "GET").upper(),
    ...
)

Changes

• src/requests/sessions.py: Added fallback to "GET" when request.method is None
• tests/test_requests.py: Added comprehensive test case test_prepare_request_with_none_method() to verify the fix and prevent regression

Testing

The new test case verifies that:

1. A Request object can be created with method=None
2. Session.prepare_request() successfully prepares the request without crashing
3. The prepared request defaults to the "GET" method
4. The URL is properly preserved

Impact

This is a bug fix that improves robustness and prevents unexpected crashes when using the library. The behavior aligns with HTTP standards where GET is the default method.

[tboy1337]

I should add that this issue was found because of I think (I'm not 100% sure because everything was also typed according to mypy rules in the commit) pylint in #7054, if it was pylint that found this issue and it is a legitimate issue then it makes a strong case for the project to start using it imo.