fix(google-genai): Guard response extraction

[alexander-alderman-webb]

Description

Both fields are declared to be optional:

https://github.com/googleapis/python-genai/blob/f4bcca45e0805c798ee86530e013a0c325d0af85/google/genai/types.py#L7485

https://github.com/googleapis/python-genai/blob/f4bcca45e0805c798ee86530e013a0c325d0af85/google/genai/types.py#L2145

Issues

Closes #5854

Reminders

• Please add tests to validate your changes, and lint your code using tox -e linters.
• Add GH Issue ID & Linear ID (if applicable)
• PR title should use conventional commit style (feat:, fix:, ref:, meta:)
• For external contributors: CONTRIBUTING.md, Sentry SDK development docs, Discord community

[github-actions]

Semver Impact of This PR

🟢 Patch (bug fixes)

📋 Changelog Preview

This is how your changes will appear in the changelog.
Entries from this PR are highlighted with a left border (blockquote style).

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New Features ✨

Langchain

• Set gen_ai.operation.name and gen_ai.pipeline.name on LLM spans by ericapisani in #5849
• Broaden AI provider detection beyond OpenAI and Anthropic by ericapisani in #5707
• Update LLM span operation to gen_ai.generate_text by ericapisani in #5796

Bug Fixes 🐛

• (google-genai) Guard response extraction by alexander-alderman-webb in #5869

Internal Changes 🔧

Langchain

• Add text completion test by alexander-alderman-webb in #5740
• Add tool execution test by alexander-alderman-webb in #5739
• Add basic agent test with Responses call by alexander-alderman-webb in #5726
• Replace mocks with httpx types by alexander-alderman-webb in #5724
• Consolidate span origin assertion by alexander-alderman-webb in #5723
• Consolidate available tools assertion by alexander-alderman-webb in #5721

Other

• (asyncpg) Normalize query whitespace in integration by ericapisani in #5855
• Add note to coordinate with assignee before PR submission by sentrivana in #5868
• Temporarily stop running litellm tests by alexander-alderman-webb in #5851

Other

• ci+docs: Add draft PR enforcement by stephanie-anderson in #5867

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_{🤖 This preview updates automatically when you update the PR.}

[github-actions]

Codecov Results 📊

✅ 13 passed | Total: 13 | Pass Rate: 100% | Execution Time: 9.08s

📊 Comparison with Base Branch

Metric	Change
Total Tests	—
Passed Tests	—
Failed Tests	—
Skipped Tests	—

✨ No test changes detected

All tests are passing successfully.

❌ Patch coverage is 0.00%. Project has 14391 uncovered lines.
✅ Project coverage is 30.23%. Comparing base (base) to head (head).

Files with missing lines (1)

File	Patch %	Lines
utils.py	0.00%	⚠️ 481 Missing

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    25.32%    30.23%    +4.91%
==========================================
  Files          189       189         —
  Lines        20625     20627        +2
  Branches      6738      6740        +2
==========================================
+ Hits          5223      6236     +1013
- Misses       15402     14391     -1011
- Partials       429       474       +45

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