Avoid breaking LINQ query expressions with nullable reference types.

ICSharpCode.Decompiler.Tests/TestCases/Pretty/NullableRefTypes.cs

@@ -3,6 +3,7 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Diagnostics.CodeAnalysis;
+using System.Linq;
 
 namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 {
@@ -207,4 +208,21 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			return default;
 		}
 	}
+
+	public class T09_Linq
+	{
+		public IEnumerable<string> QueryWithNonNullableReferenceTypes(IEnumerable<string> strings)
+		{
+			return from s in strings
+				   where s.Length > 0
+				   select s.ToUpper();
+		}
+
+		public IEnumerable<string> QueryWithNullableReferenceTypes(IEnumerable<string?> strings)
+		{
+			return from s in strings
+				   where s != null
+				   select s.ToUpper();
+		}
+	}
 }

ICSharpCode.Decompiler/Semantics/LambdaResolveResult.cs

@@ -165,7 +165,7 @@ namespace ICSharpCode.Decompiler.Semantics
 					return Conversion.None;
 				for (int i = 0; i < parameterTypes.Length; ++i)
 				{
-					if (parameterTypes[i].Equals(this.Parameters[i].Type))
+					if (NormalizeTypeVisitor.IgnoreNullability.EquivalentTypes(parameterTypes[i], this.Parameters[i].Type))
 					{
 						continue;
 					}