From 83c71d9aa59268cf488a769b72ca2298148c8794 Mon Sep 17 00:00:00 2001
From: Owen Smith <owen@omsmith.ca>
Date: Thu, 10 Sep 2026 08:34:59 -0400
Subject: [PATCH] PatternString: treat null values as non-passing

Currently crashes. Maybe we consider adding an AllowNulls to the attribute
---
 .../PatternStringAttributeAnalyzer.cs                    | 2 +-
 .../Specs/PatternStringAttributeAnalyzer.cs              | 9 +++++++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/Rules/D2L.CodeStyle.Analyzers.Rule.PatternString/PatternStringAttributeAnalyzer.cs b/src/Rules/D2L.CodeStyle.Analyzers.Rule.PatternString/PatternStringAttributeAnalyzer.cs
index 80f45863..c1439dc6 100644
--- a/src/Rules/D2L.CodeStyle.Analyzers.Rule.PatternString/PatternStringAttributeAnalyzer.cs
+++ b/src/Rules/D2L.CodeStyle.Analyzers.Rule.PatternString/PatternStringAttributeAnalyzer.cs
@@ -249,7 +249,7 @@ ConcurrentDictionary<string, Lazy<Regex>> regexCache
 		// [PatternString] requires the assigned value to be a compile-time
 		// constant so that we can evaluate it here.
 		Optional<object?> constant = valueOperation.ConstantValue;
-		if( !constant.HasValue ) {
+		if( !constant.HasValue || constant.Value is null ) {
 			context.ReportDiagnostic(
 				Diagnostic.Create(
 					descriptor: Diagnostics.PatternStringMustBeConstant,
diff --git a/tests/D2L.CodeStyle.Analyzers.Test/Specs/PatternStringAttributeAnalyzer.cs b/tests/D2L.CodeStyle.Analyzers.Test/Specs/PatternStringAttributeAnalyzer.cs
index c13ac2c5..c4cd295b 100644
--- a/tests/D2L.CodeStyle.Analyzers.Test/Specs/PatternStringAttributeAnalyzer.cs
+++ b/tests/D2L.CodeStyle.Analyzers.Test/Specs/PatternStringAttributeAnalyzer.cs
@@ -98,14 +98,19 @@ void SinglePatternTests() {
 		}
 
 		void NonConstantValuesAreFlagged() {
-
+			#region Non-constant values are flagged as needing to be constant
 			string variable = "123";
 
-			#region Non-constant values are flagged as needing to be constant
 			Digits _ = new( /* PatternStringMustBeConstant() */ variable /**/ );
 			Digits _ = /* PatternStringMustBeConstant() */ variable /**/;
 			_ = (Digits)/* PatternStringMustBeConstant() */ variable /**/;
 			#endregion
+
+			#region null is treated as non-constant
+			Digits _ = new( /* PatternStringMustBeConstant() */ null /**/ );
+			Digits _ = /* PatternStringMustBeConstant() */ null /**/;
+			_ = (Digits)/* PatternStringMustBeConstant() */ null /**/;
+			#endregion
 		}
 
 		void MultiplePatternTests() {