fix: guard against null source in SingleOrDefaultIfMultiple

[ANcpLua]

SingleOrDefaultIfMultiple<T> calls source.GetEnumerator() without validating source, so passing null throws a NullReferenceException.

Every other public entry point in EnumerableExtensions.Single — Only, Only(predicate), OnlyOrDefault, OnlyOrDefault(predicate) — routes through TryOnly, which calls Guard.NotNull(source) and throws a clean ArgumentNullException. This makes SingleOrDefaultIfMultiple the odd one out.

This adds the same Guard.NotNull(source) guard so the null-argument contract is consistent across the file. No behavior change for non-null inputs.

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999.9.9


10.0.203
latestMinor

<PropertyGroup Label="Roslyn">
    <RoslynVersion>5.3.0</RoslynVersion>
    <RoslynAnalyzersVersion>5.3.0</RoslynAnalyzersVersion>
</PropertyGroup>

<!-- ═══════════════════════════════════════════════════════════════════════
     ROSLYN ANALYZER TESTING
     Used by: Roslyn.Utilities.Testing, Analyzers.Tests
     ════════════════════════════════════════════════════════════════════...

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• src/ANcpLua.Roslyn.Utilities/EnumerableExtensions.Single.cs

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src/ANcpLua.Roslyn.Utilities/EnumerableExtensions.Single.cs (1)

26-27: LGTM!

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Summary by CodeRabbit

• Bug Fixes
  • Improved input validation for a sequence helper so null values are handled immediately with a clear guard check instead of failing later during processing.

Walkthrough

Adds a Guard.NotNull(source) call at the top of SingleOrDefaultIfMultiple<T> in EnumerableExtensions.Single.cs to explicitly validate the source parameter before enumeration begins.

Null Guard Addition

Layer / File(s)	Summary
Null guard enforcement src/ANcpLua.Roslyn.Utilities/EnumerableExtensions.Single.cs	Guard.NotNull(source) inserted before GetEnumerator() so null input throws eagerly with a clear error instead of a deferred NullReferenceException.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~2 minutes

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Important

Pre-merge checks failed

Please resolve all errors before merging. Addressing warnings is optional.

❌ Failed checks (1 error)

Check name	Status	Explanation	Resolution
Title check	❌ Error	The title matches the change, but it violates the required conventional-commit scope format.	Use a title like fix(<scope>): guard against null source in SingleOrDefaultIfMultiple with one of the required scopes.

✅ Passed checks (7 passed)

Check name	Status	Explanation
Description check	✅ Passed	The description clearly matches the null-guard fix in SingleOrDefaultIfMultiple.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Otel Instrumentation Required	✅ Passed	Only a static EnumerableExtensions file changed; no new DI-registered service class, ActivitySource, or Meter was added.
No Unbounded Mcp Responses	✅ Passed	No src/qyl.mcp paths or MCP tool definitions exist in this PR, so the bounded-response check is not applicable.
Duckdb Backpressure On Write Paths	✅ Passed	The PR only adds a null guard in EnumerableExtensions.Single.cs; no new DuckDB write path is introduced.
Cancellationtoken Threading	✅ Passed	No new public async methods were added; the only modified method is synchronous and only adds a null guard.

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