fix: fix mypy

[parthea]

Towards #15104

This is needed to unblock #15457 .

See follow up issue googleapis/proto-plus-python#558 for the prerelease presubmit failure.

See the following mypy failure for grafeas

2026-01-16T22:02:28.7158467Z grafeas/grafeas_v1/services/grafeas/client.py:362: error: Incompatible default for argument "transport" (default has type "None", argument has type "str | GrafeasTransport") 

[gemini-code-assist]

Summary of Changes

Hello @parthea, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request focuses on resolving mypy type checking issues by refining the type annotation for the transport parameter within the GrafeasClient initialization. By explicitly marking this parameter as Optional, the code now correctly communicates that None is an acceptable value, leading to cleaner static analysis results and improved code clarity.

Highlights

• Type Hint Correction: The type annotation for the transport parameter in the GrafeasClient constructor has been updated to explicitly include Optional. This change ensures that the parameter can correctly accept None as a value.
• Mypy Compliance: This modification addresses mypy static analysis warnings or errors by providing a more accurate type hint, improving the overall type-checking integrity of the codebase.

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[gemini-code-assist]

Code Review

This pull request fixes a mypy issue by explicitly defining the transport parameter as Optional. The change is correctly applied to both the generator configuration and the resulting Python client code, ensuring consistency. The change is straightforward and improves type hint clarity. Looks good to me.