Fix all build warnings (unreachable code, nullable refs, and MSTEST)

[Copilot]

Summary

Fixes all 26 build warnings by addressing unreachable code, nullable reference issues, and obsolete MSTest attributes.

Problem

The build was generating 26 warnings:

• 1 CS0162 warning due to unreachable code in GitVersionStartupService
• 7 CS8602/CS8625 warnings for nullable reference dereferences
• 12 MSTEST0039 warnings for using obsolete Assert.ThrowsException
• 6 MSTEST0044 warnings for using obsolete DataTestMethod attribute

Solution

1. Unreachable Code (CS0162)

Following the issue requirement that "unreachable code should be commented and not deleted, as it might have a meaning":

• Commented out the unreachable code block (lines 31-40) instead of removing it
• Added explanatory comments documenting why the code is preserved:
  • The code searches for git installations in a "Gits" folder
  • It selects the best version from multiple git installations
  • It may be needed when supporting multiple git versions or custom git installations

2. Nullable Reference Warnings (CS8602/CS8625)

• Added null-conditional operators (?.) for operations that could return null
• Used null-forgiving operator (!) where values are guaranteed to be non-null in test contexts
• Added proper null checks in benchmark code

3. MSTest Warnings (MSTEST0039 & MSTEST0044)

• Replaced Assert.ThrowsException with Assert.ThrowsExactly for more precise exception type checking
• Replaced Assert.ThrowsExceptionAsync with Assert.ThrowsExactlyAsync
• Replaced obsolete [DataTestMethod] attribute with [TestMethod] (DataRow attributes continue to work correctly)

Changes

• Modified: Gibbon.Git.Server/Git/GitVersionService/GitVersionStartupService.cs
• Modified: Gibbon.Git.Server.Benchmarks/Program.cs
• Modified: 15 test files to fix nullable reference and MSTest warnings

Testing

• ✅ Build now completes with 0 warnings (down from 26)
• ✅ All 254 tests pass (237 unit tests + 17 integration tests)
• ✅ No functional changes - the behavior remains identical

Impact

This is a minimal, non-breaking change that eliminates all build warnings while preserving potentially useful code for future enhancements and improving test code quality.

Fixes #80

Original prompt

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This section details on the original issue you should resolve

<issue_title>Fix warning on build</issue_title>
<issue_description>As title describes, fix warnings on build.
Unreachable code should be commented and not deleted, as it might have a meaning. </issue_description>

Comments on the Issue (you are @copilot in this section)

Fixes #80

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[Matt-17]

@copilot You missed all the other warnings ;-)

[Copilot]

@copilot You missed all the other warnings ;-)

Fixed all 25 remaining warnings in commit a33b208:

• 7 nullable reference warnings (CS8602/CS8625)
• 12 MSTEST0039 warnings (ThrowsException → ThrowsExactly)
• 6 MSTEST0044 warnings (DataTestMethod → TestMethod)

Build now completes with 0 warnings, all 254 tests passing.