IntelliTect · BenjaminMichaelis · Feb 24, 2026 · Mar 9, 2026 · Mar 9, 2026 · Mar 10, 2026
diff --git a/Directory.Build.props b/Directory.Build.props
@@ -2,5 +2,6 @@
   <PropertyGroup>
     <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
     <LangVersion>14.0</LangVersion>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 </Project>
diff --git a/IntelliTect.Analyzer/IntelliTect.Analyzer.CodeFixes/AsyncVoid.cs b/IntelliTect.Analyzer/IntelliTect.Analyzer.CodeFixes/AsyncVoid.cs
@@ -26,13 +26,21 @@ public sealed override FixAllProvider GetFixAllProvider()
 
         public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
         {
-            SyntaxNode root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+            SyntaxNode? root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+            if (root is null)
+            {
+                return;
+            }
 
             Diagnostic diagnostic = context.Diagnostics.First();
             Microsoft.CodeAnalysis.Text.TextSpan diagnosticSpan = diagnostic.Location.SourceSpan;
 
             // Find the type declaration identified by the diagnostic.
             var declaration = root.FindToken(diagnosticSpan.Start).Parent as MethodDeclarationSyntax;
+            if (declaration is null)
+            {
+                return;
+            }
 
             // Register a code action that will invoke the fix.
             context.RegisterCodeFix(
@@ -45,7 +53,8 @@ public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
 
         private static async Task<Document> MakeReturnTask(Document document, MethodDeclarationSyntax declaration, CancellationToken cancellationToken)
         {
-            SyntaxNode root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
+            SyntaxNode root = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false)
+                ?? throw new System.InvalidOperationException("Could not get syntax root");
             SyntaxNode newRoot = root.ReplaceNode(declaration.ReturnType, SyntaxFactory.ParseTypeName(typeof(Task).Name).WithTrailingTrivia(SyntaxFactory.Space));
             return document.WithSyntaxRoot(newRoot);
         }

diff --git a/IntelliTect.Analyzer/IntelliTect.Analyzer.CodeFixes/AttributesOnSeparateLines.cs b/IntelliTect.Analyzer/IntelliTect.Analyzer.CodeFixes/AttributesOnSeparateLines.cs
@@ -29,7 +29,11 @@ public sealed override FixAllProvider GetFixAllProvider()
 
         public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
         {
-            SyntaxNode root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+            SyntaxNode? root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+            if (root is null)
+            {
+                return;
+            }
 
             Diagnostic diagnostic = context.Diagnostics.First();
             Microsoft.CodeAnalysis.Text.TextSpan diagnosticSpan = diagnostic.Location.SourceSpan;
@@ -38,14 +42,17 @@ public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
             SyntaxToken declaration = root.FindToken(diagnosticSpan.Start);
 
             // Find the enclosing AttributeList
-            SyntaxNode attributeList = declaration.Parent;
-            while (!attributeList.IsKind(SyntaxKind.AttributeList))
+            SyntaxNode? attributeList = declaration.Parent;
+            while (attributeList is not null && !attributeList.IsKind(SyntaxKind.AttributeList))
             {
                 attributeList = attributeList.Parent;
             }
 
             // Get the class, method or property adjacent to the AttributeList
-            SyntaxNode parentDeclaration = attributeList.Parent;
+            if (attributeList?.Parent is not SyntaxNode parentDeclaration)
+            {
+                return;
+            }
 
             // Register a code action that will invoke the fix.
             context.RegisterCodeFix(
@@ -78,7 +85,8 @@ private static async Task<Document> PutOnSeparateLine(Document document, SyntaxN
                 .WithAdditionalAnnotations(Formatter.Annotation);
 
             // Replace the old local declaration with the new local declaration.
-            SyntaxNode oldRoot = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
+            SyntaxNode oldRoot = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false)
+                ?? throw new InvalidOperationException("Could not get syntax root");
             SyntaxNode newRoot = oldRoot.ReplaceNode(parentDeclaration, newNode);
 
             return document.WithSyntaxRoot(newRoot);

diff --git a/IntelliTect.Analyzer/IntelliTect.Analyzer.CodeFixes/FavorDirectoryEnumerationCalls.cs b/IntelliTect.Analyzer/IntelliTect.Analyzer.CodeFixes/FavorDirectoryEnumerationCalls.cs
@@ -30,16 +30,24 @@ public sealed override FixAllProvider GetFixAllProvider() =>
 
         public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
         {
-            SyntaxNode root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+            SyntaxNode? root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+            if (root is null)
+            {
+                return;
+            }
 
             Diagnostic diagnostic = context.Diagnostics.First();
             TextSpan diagnosticSpan = diagnostic.Location.SourceSpan;
 
             // The diagnostic span covers the full invocation expression (Directory.GetFiles(...))
-            InvocationExpressionSyntax invocation = root.FindToken(diagnosticSpan.Start)
-                .Parent.AncestorsAndSelf()
+            InvocationExpressionSyntax? invocation = root.FindToken(diagnosticSpan.Start)
+                .Parent?.AncestorsAndSelf()
                 .OfType<InvocationExpressionSyntax>()
-                .First();
+                .FirstOrDefault();
+            if (invocation is null)
+            {
+                return;
+            }
 
             bool isGetFiles = diagnostic.Id == Analyzers.FavorDirectoryEnumerationCalls.DiagnosticId301;
             string title = isGetFiles ? TitleGetFiles : TitleGetDirectories;
@@ -61,7 +69,7 @@ private static async Task<Document> UseEnumerationMethodAsync(
         {
             var memberAccess = (MemberAccessExpressionSyntax)invocation.Expression;
 
-            SemanticModel semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
+            SemanticModel? semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
 
             // Rename: Directory.GetFiles(...) → Directory.EnumerateFiles(...)
             InvocationExpressionSyntax renamedInvocation = invocation.WithExpression(
@@ -76,7 +84,8 @@ private static async Task<Document> UseEnumerationMethodAsync(
                         SyntaxFactory.IdentifierName("ToArray")))
                 : renamedInvocation;
 
-            SyntaxNode oldRoot = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false);
+            SyntaxNode oldRoot = await document.GetSyntaxRootAsync(cancellationToken).ConfigureAwait(false)
+                ?? throw new System.InvalidOperationException("Could not get syntax root");
             SyntaxNode newRoot = oldRoot.ReplaceNode(invocation, replacement.WithAdditionalAnnotations(Formatter.Annotation));
 
             if (replacement != renamedInvocation && newRoot is CompilationUnitSyntax compilationUnit)
@@ -89,10 +98,14 @@ private static async Task<Document> UseEnumerationMethodAsync(
 
         private static bool NeedsToArrayWrapper(
             InvocationExpressionSyntax invocation,
-            SemanticModel semanticModel,
+            SemanticModel? semanticModel,
             CancellationToken ct)
         {
-            SyntaxNode parent = invocation.Parent;
+            if (semanticModel is null)
+            {
+                return false;
+            }
+            SyntaxNode? parent = invocation.Parent;
 
             // string[] files = Directory.GetFiles(...)  or field/property initializer
             if (parent is EqualsValueClauseSyntax equalsValue)
@@ -123,7 +136,7 @@ private static bool NeedsToArrayWrapper(
             // return Directory.GetFiles(...)  in a method or local function returning string[]
             if (parent is ReturnStatementSyntax)
             {
-                TypeSyntax returnType = invocation.Ancestors()
+                TypeSyntax? returnType = invocation.Ancestors()
                     .Select(a => a switch
                     {
                         MethodDeclarationSyntax m => m.ReturnType,
@@ -141,7 +154,7 @@ private static bool NeedsToArrayWrapper(
             // Expression-bodied members: string[] GetFiles() => Directory.GetFiles(...)
             if (parent is ArrowExpressionClauseSyntax arrow)
             {
-                TypeSyntax returnType = arrow.Parent switch
+                TypeSyntax? returnType = arrow.Parent switch
                 {
                     MethodDeclarationSyntax m => m.ReturnType,
                     LocalFunctionStatementSyntax lf => lf.ReturnType,
@@ -160,7 +173,7 @@ private static bool NeedsToArrayWrapper(
                 && argumentList.Parent is InvocationExpressionSyntax outerInvocation
                 && semanticModel.GetSymbolInfo(outerInvocation, ct).Symbol is IMethodSymbol outerMethod)
             {
-                IParameterSymbol targetParam;
+                IParameterSymbol? targetParam;
 
                 // Named argument: SomeMethod(param: Directory.GetFiles(...))
                 if (argument.NameColon != null)

diff --git a/IntelliTect.Analyzer/IntelliTect.Analyzer.CodeFixes/NamingFieldPascalUnderscore.cs b/IntelliTect.Analyzer/IntelliTect.Analyzer.CodeFixes/NamingFieldPascalUnderscore.cs
@@ -27,7 +27,11 @@ public sealed override FixAllProvider GetFixAllProvider()
 
         public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
         {
-            SyntaxNode root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+            SyntaxNode? root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+            if (root is null)
+            {
+                return;
+            }
 
             Diagnostic diagnostic = context.Diagnostics.First();
             TextSpan diagnosticSpan = diagnostic.Location.SourceSpan;
@@ -50,8 +54,16 @@ private static async Task<Solution> MakePascalWithUnderscore(Document document,
             string nameWithoutUnderscore = nameOfField.TrimStart('_');
             string newName = "_" + char.ToUpper(nameWithoutUnderscore.First()) + nameWithoutUnderscore.Substring(1);
 
-            SemanticModel semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
-            ISymbol symbol = semanticModel.GetDeclaredSymbol(declaration.Parent, cancellationToken);
+            SemanticModel? semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
+            if (semanticModel is null || declaration.Parent is null)
+            {
+                return document.Project.Solution;
+            }
+            ISymbol? symbol = semanticModel.GetDeclaredSymbol(declaration.Parent, cancellationToken);
+            if (symbol is null)
+            {
+                return document.Project.Solution;
+            }
             Solution solution = document.Project.Solution;
             SymbolRenameOptions options = new()
             {

diff --git a/IntelliTect.Analyzer/IntelliTect.Analyzer.CodeFixes/NamingIdentifierPascal.cs b/IntelliTect.Analyzer/IntelliTect.Analyzer.CodeFixes/NamingIdentifierPascal.cs
@@ -27,7 +27,11 @@ public sealed override FixAllProvider GetFixAllProvider()
 
         public sealed override async Task RegisterCodeFixesAsync(CodeFixContext context)
         {
-            SyntaxNode root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+            SyntaxNode? root = await context.Document.GetSyntaxRootAsync(context.CancellationToken).ConfigureAwait(false);
+            if (root is null)
+            {
+                return;
+            }
 
             Diagnostic diagnostic = context.Diagnostics.First();
             TextSpan diagnosticSpan = diagnostic.Location.SourceSpan;
@@ -49,8 +53,16 @@ private static async Task<Solution> MakePascal(Document document, SyntaxToken de
             string nameOfField = declaration.ValueText;
             string newName = char.ToUpper(nameOfField.First()) + nameOfField.Substring(1);
 
-            SemanticModel semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
-            ISymbol symbol = semanticModel.GetDeclaredSymbol(declaration.Parent, cancellationToken);
+            SemanticModel? semanticModel = await document.GetSemanticModelAsync(cancellationToken).ConfigureAwait(false);
+            if (semanticModel is null || declaration.Parent is null)
+            {
+                return document.Project.Solution;
+            }
+            ISymbol? symbol = semanticModel.GetDeclaredSymbol(declaration.Parent, cancellationToken);
+            if (symbol is null)
+            {
+                return document.Project.Solution;
+            }
             Solution solution = document.Project.Solution;
             SymbolRenameOptions options = new()
             {

diff --git a/IntelliTect.Analyzer/IntelliTect.Analyzer.Integration.Tests/AnalyzerTests.cs b/IntelliTect.Analyzer/IntelliTect.Analyzer.Integration.Tests/AnalyzerTests.cs
@@ -34,7 +34,9 @@ public static async Task ProcessProject(FileInfo projectFile)
             using var workspace = MSBuildWorkspace.Create();
             Project project = await workspace.OpenProjectAsync(projectFile.FullName).ConfigureAwait(false);
 
-            CompilationWithAnalyzers compilationWithAnalyzers = (await project.GetCompilationAsync().ConfigureAwait(false))
+            Compilation compilation = await project.GetCompilationAsync().ConfigureAwait(false)
+                ?? throw new InvalidOperationException("Could not get compilation");
+            CompilationWithAnalyzers compilationWithAnalyzers = compilation
                 .WithAnalyzers(ImmutableArray.Create(GetAnalyzers().ToArray()));
 
             ImmutableArray<Diagnostic> diags = await compilationWithAnalyzers.GetAnalyzerDiagnosticsAsync().ConfigureAwait(false);

diff --git a/IntelliTect.Analyzer/IntelliTect.Analyzer.Test/Helpers/CodeFixVerifier.Helper.cs b/IntelliTect.Analyzer/IntelliTect.Analyzer.Test/Helpers/CodeFixVerifier.Helper.cs
@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
@@ -26,7 +27,8 @@ private static async Task<Document> ApplyFix(Document document, CodeAction codeA
         {
             System.Collections.Immutable.ImmutableArray<CodeActionOperation> operations = await codeAction.GetOperationsAsync(CancellationToken.None);
             Solution solution = operations.OfType<ApplyChangesOperation>().Single().ChangedSolution;
-            return solution.GetDocument(document.Id);
+            return solution.GetDocument(document.Id)
+                ?? throw new InvalidOperationException("Could not get document from solution");
         }
 
         /// <summary>
@@ -66,7 +68,8 @@ private static IEnumerable<Diagnostic> GetNewDiagnostics(IEnumerable<Diagnostic>
         /// <returns>The compiler diagnostics that were found in the code</returns>
         private static IEnumerable<Diagnostic> GetCompilerDiagnostics(Document document)
         {
-            return document.GetSemanticModelAsync().Result.GetDiagnostics();
+            return (document.GetSemanticModelAsync().Result
+                ?? throw new InvalidOperationException("Could not get semantic model")).GetDiagnostics();
         }
 
         /// <summary>
@@ -77,7 +80,8 @@ private static IEnumerable<Diagnostic> GetCompilerDiagnostics(Document document)
         private static string GetStringFromDocument(Document document)
         {
             Document simplifiedDoc = Simplifier.ReduceAsync(document, Simplifier.Annotation).Result;
-            SyntaxNode root = simplifiedDoc.GetSyntaxRootAsync().Result;
+            SyntaxNode root = simplifiedDoc.GetSyntaxRootAsync().Result
+                ?? throw new InvalidOperationException("Could not get syntax root");
             root = Formatter.Format(root, Formatter.Annotation, simplifiedDoc.Project.Solution.Workspace);
             return root.GetText().ToString();
         }

diff --git a/IntelliTect.Analyzer/IntelliTect.Analyzer.Test/Helpers/DiagnosticVerifier.Helper.cs b/IntelliTect.Analyzer/IntelliTect.Analyzer.Test/Helpers/DiagnosticVerifier.Helper.cs
@@ -22,11 +22,11 @@ public abstract partial class DiagnosticVerifier
         private static readonly MetadataReference _CSharpSymbolsReference = MetadataReference.CreateFromFile(typeof(CSharpCompilation).Assembly.Location);
         private static readonly MetadataReference _CodeAnalysisReference = MetadataReference.CreateFromFile(typeof(Compilation).Assembly.Location);
         private static readonly MetadataReference _LinqExpressionsReference = MetadataReference.CreateFromFile(typeof(Expression<>).Assembly.Location);
-        private static readonly MetadataReference _SystemRuntimeReference = GetSystemRuntimeReference();
+        private static readonly MetadataReference? _SystemRuntimeReference = GetSystemRuntimeReference();
 
-        private static MetadataReference GetSystemRuntimeReference()
+        private static MetadataReference? GetSystemRuntimeReference()
         {
-            string runtimeDir = Path.GetDirectoryName(typeof(object).Assembly.Location);
+            string? runtimeDir = Path.GetDirectoryName(typeof(object).Assembly.Location);
             if (string.IsNullOrEmpty(runtimeDir))
             {
                 return null;
@@ -76,7 +76,9 @@ protected static Diagnostic[] GetSortedDiagnosticsFromDocuments(DiagnosticAnalyz
             var diagnostics = new List<Diagnostic>();
             foreach (Project project in projects)
             {
-                CompilationWithAnalyzers compilationWithAnalyzers = project.GetCompilationAsync().Result.WithAnalyzers(ImmutableArray.Create(analyzer));
+                CompilationWithAnalyzers compilationWithAnalyzers = (project.GetCompilationAsync().Result
+                    ?? throw new InvalidOperationException("Could not get compilation"))
+                    .WithAnalyzers(ImmutableArray.Create(analyzer));
                 ImmutableArray<Diagnostic> diags = compilationWithAnalyzers.GetAnalyzerDiagnosticsAsync().Result;
                 foreach (Diagnostic diag in diags)
                 {
@@ -89,7 +91,7 @@ protected static Diagnostic[] GetSortedDiagnosticsFromDocuments(DiagnosticAnalyz
                         for (int i = 0; i < documents.Length; i++)
                         {
                             Document document = documents[i];
-                            SyntaxTree tree = document.GetSyntaxTreeAsync().Result;
+                            SyntaxTree? tree = document.GetSyntaxTreeAsync().Result;
                             if (tree == diag.Location.SourceTree)
                             {
                                 diagnostics.Add(diag);
@@ -193,7 +195,8 @@ private static Project CreateProject(string[] sources, string language = Languag
                 count++;
             }
 
-            return solution.GetProject(projectId);
+            return solution.GetProject(projectId)
+                ?? throw new InvalidOperationException("Could not get project from solution");
         }
         #endregion
     }