feat: Enables Nullable Reference Types

[BenjaminMichaelis]

No description provided.

[Copilot]

Pull request overview

This PR enables Nullable Reference Types (NRT) across the entire IntelliTect.Analyzer codebase by adding <Nullable>enable</Nullable> to Directory.Build.props and updating all affected code to properly handle nullable annotations. The changes ensure type safety by explicitly marking nullable types and adding appropriate null checks throughout the codebase.

Changes:

• Enabled nullable reference types in Directory.Build.props for all projects
• Updated analyzers with nullable annotations and null safety checks
• Enhanced code fixes with proper nullable handling and graceful degradation patterns
• Improved test infrastructure with nullable annotations and ArgumentNullException.ThrowIfNull validation

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
Directory.Build.props	Added <Nullable>enable</Nullable> to enable nullable reference types project-wide
UnusedLocalVariable.cs	Added null check for DataFlowAnalysis result from AnalyzeDataFlow
BanImplicitDateTimeToDateTimeOffsetConversion.cs	Added nullable annotation to GetTypeByMetadataName result
AttributesOnSeparateLines.cs (Analyzer)	Added null checks for ApplicationSyntaxReference and null-conditional operator for AttributeClass.Name
AsyncVoid.cs (Analyzer)	Improved pattern matching using is not pattern for cleaner null handling
AnalyzerBlockMixins.cs	Updated return types and intermediate variables with nullable annotations
DiagnosticVerifier.cs	Added nullable annotations and ArgumentNullException.ThrowIfNull validation
CodeFixVerifier.cs	Added nullable annotations, ArgumentNullException.ThrowIfNull, and null-forgiving operators on Task.Result
DiagnosticVerifier.Helper.cs	Added null checks with InvalidOperationException for compilation operations
CodeFixVerifier.Helper.cs	Added null checks with InvalidOperationException for document and semantic model operations
AnalyzerTests.cs	Added null check for compilation result
NamingIdentifierPascal.cs	Added graceful degradation by returning original solution when null checks fail
NamingFieldPascalUnderscore.cs	Added graceful degradation by returning original solution when null checks fail
AttributesOnSeparateLines.cs (CodeFix)	Added null checks for syntax root and null-forgiving operators for Parent navigation
AsyncVoid.cs (CodeFix)	Added null checks for syntax root and method declaration

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Copilot]

Inconsistent null handling compared to the AnalyzeObjectCreation method in the same file. While SymbolEqualityComparer.Default.Equals correctly handles null values and returns false, the AnalyzeObjectCreation method (lines 62-65) throws an InvalidOperationException if GetTypeByMetadataName returns null. Consider adding a similar null check here for consistency, or at minimum add a comment explaining why the different approaches are acceptable.