Enable nullable types in Linux detector files

[jasonpaulos]

Enable nullable types in Linux detector files

[github-actions]

👋 Hi! It looks like you modified some files in the Detectors folder.
You may need to bump the detector versions if any of the following scenarios apply:

• The detector detects more or fewer components than before
• The detector generates different parent/child graph relationships than before
• The detector generates different devDependencies values than before

If none of the above scenarios apply, feel free to ignore this comment 🙂

[Copilot]

Pull request overview

This PR enables nullable reference types across all Linux detector files by removing #nullable disable directives and adding the necessary nullable annotations to maintain type safety. This is part of the broader effort to enable nullable types throughout the codebase (as indicated by Nullable=enable in Directory.Build.props).

Changes:

• Removed #nullable disable from all source files under src/Microsoft.ComponentDetection.Detectors/linux/ and their corresponding test files
• Added nullable annotations (? and !) to return types, parameters, and local variables where needed (e.g., factory CreateComponent methods now return TypedComponent?, helper methods return string?)
• Updated test files to use null! instead of null for non-nullable constructor parameters and added NotBeNull() assertions where needed

Reviewed changes

Copilot reviewed 20 out of 20 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/.../linux/ILinuxScanner.cs	Removed #nullable disable
src/.../linux/LinuxScanner.cs	Removed #nullable disable; added null-forgiving ! after .Where() filter; changed error return from null to []; made CreateComponentWithLayers return tuple TypedComponent?
src/.../linux/LinuxContainerDetector.cs	Removed #nullable disable; added ! to Enum.GetName; simplified InvalidUserInputException to single-param ctor
src/.../linux/LinuxApplicationLayerDetector.cs	Removed #nullable disable; added ! to all Enum.GetName calls
src/.../linux/Contracts/ImageScanningResult.cs	Removed #nullable disable; ContainerDetails → ContainerDetails?; Components initialized to []
src/.../linux/Exceptions/MissingContainerDetailException.cs	Removed #nullable disable
src/.../linux/Factories/IArtifactComponentFactory.cs	Removed #nullable disable; CreateComponent returns TypedComponent?
src/.../linux/Factories/ArtifactComponentFactoryBase.cs	Removed #nullable disable; abstract CreateComponent returns TypedComponent?; helper methods return string?
src/.../linux/Factories/*.cs (9 factories)	Removed #nullable disable; CreateComponent overrides return TypedComponent?; private helper return types updated
test/.../LinuxScannerTests.cs	Removed #nullable disable; added BeOfType and NotBeNull assertions
test/.../LinuxContainerDetectorTests.cs	Removed #nullable disable; updated Func<..., Exception?, string> in mock verifications
test/.../LinuxApplicationLayerExperimentTests.cs	Removed #nullable disable; changed null to null! for constructor args

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 0.0%. Comparing base (3d2cdeb) to head (79ef6a6).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@     Coverage Diff      @@
##   main   #1709   +/-   ##
============================
============================

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.