fix(event_handler): skip compression when the response has no body

[Om-singhaI]

Issue number: closes #8484

Summary

Changes

ResponseBuilder._compress sets Content-Encoding: gzip, converts a str body to bytes, then hands the body to zlib. A Response built without a body still has body=None at that point, so zlib raises TypeError: a bytes-like object is required, not 'NoneType'. The error escapes app.resolve() and the invocation fails, so API Gateway answers 502 instead of the 204 or 304 the route returned. Browsers and SDKs always send Accept-Encoding: gzip, so an affected route fails on every request.

It takes both compression enabled and an explicit Response with no body. Returning None or (None, 204) from a route is serialized to "null" before compression, so those never crashed. ALBResolver was already safe, since #8194 replaces a None body with "".

• _compress now returns early when self.response.body is None, with a debug log, so Content-Encoding is not set on a response that has nothing to encode.
• Nothing else changes. An empty string body is still compressed exactly as before, and so is every non empty body.
• Four new functional tests in tests/functional/event_handler/required_dependencies/test_api_gateway.py: a compress=True route returning Response(204) and Response(304), Response(status_code=204, compress=True) on a route that does not set compress, and an exception handler returning a Response with no body under a compress=True route.

User experience

Before: a compress=True route returning Response(status_code=204) raises TypeError: a bytes-like object is required, not 'NoneType' and the client gets 502 Internal server error.

After: the same route returns 204 with a null body and no Content-Encoding header. 304 and status only exception handler responses behave the same way, and responses that do have a body are still gzipped.

Testing:

• The four new tests fail on develop with TypeError: a bytes-like object is required, not 'NoneType' raised inside _compress, and pass here.
• tests/functional/event_handler/required_dependencies/test_api_gateway.py: 99 passed. The 11 tests matching -k compress in that file all pass.
• tests/functional/event_handler/required_dependencies: 435 passed, 1 skipped. tests/functional/event_handler/_pydantic: 437 passed.
• ruff format --check aws_lambda_powertools tests examples: 1296 files already formatted. ruff check aws_lambda_powertools tests examples: all checks passed. Ruff 0.16.7, inside the range pyproject.toml pins.
• mypy aws_lambda_powertools/event_handler/api_gateway.py: no new errors. The only two it reports are missing boto3 and botocore stubs in my local environment, in other modules, and they show up on develop too.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.80%. Comparing base (c8d9937) to head (e46fd0b).
⚠️ Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #8485   +/-   ##
========================================
  Coverage    96.79%   96.80%           
========================================
  Files          310      310           
  Lines        15531    15534    +3     
  Branches      1352     1353    +1     
========================================
+ Hits         15034    15037    +3     
  Misses         361      361           
  Partials       136      136           

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[leandrodamascena]

Thanks @Om-singhaI for finding and fixing this. The fix makes sense, and the tests cover the affected cases. Approved!

[mergify]

This pull request does not currently match the merge queue conditions, so it cannot be queued from here. The box comes back if it matches again.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[powertools-for-aws-oss-automation]

Awesome work, congrats on your first merged pull request and thank you for helping improve everyone's experience!

[boring-cyborg]

Awesome work, congrats on your first merged pull request and thank you for helping improve everyone's experience!