[yaml] - fix post commit yaml test

[derrickaw]

Fixes failures seen here
Problem: _fields doesn't exist in row and I forgot that e2e is part of post commit, so we missed this check during the last PR. My bad.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.93%. Comparing base (76f6e6d) to head (14195b6).
⚠️ Report is 211 commits behind head on master.

Additional details and impacted files

@@              Coverage Diff              @@
##             master   #40633       +/-   ##
=============================================
+ Coverage     56.16%   79.93%   +23.76%     
=============================================
  Files          1124      488      -636     
  Lines        178336    82557    -95779     
  Branches       1489        0     -1489     
=============================================
- Hits         100170    65990    -34180     
+ Misses        75645    16567    -59078     
+ Partials       2521        0     -2521     

Flag	Coverage Δ
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java	?
python	79.93% <ø> (+0.37%)	⬆️

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[derrickaw]

/gemini review

[github-actions]

📋 Review Summary

This PR fixes a failing post-commit YAML end-to-end test (gcs_avro_to_cloud_bigtable.yaml) by replacing row._fields membership checks with hasattr(row, ...) when checking for field presence in MapToFields callables.

🔍 General Feedback

• Switching from _fields (an implementation detail not present on all row/namedtuple representations) to hasattr is a clean and idiomatic way to check attribute presence on Beam Row objects in Python callables.
• No issues found; the changes look good.

---

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[github-actions]

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[shunping]

I saw you triggerred the precommit yaml test, could you trigger the postcommit one (.github/workflows/beam_PostCommit_Yaml_Xlang_Direct.yml) as well? Thanks!

[shunping]

LGTM, thanks!