Null-check conversion group nested in identity conversion (#41886)

src/Compilers/CSharp/Portable/FlowAnalysis/NullableWalker.cs

@@ -5770,8 +5770,8 @@ private static BoundConversion GetConversionIfApplicable(BoundExpression convers
                     // and that any warnings caught by this recursive call of VisitConversion won't be redundant.
                     if (useLegacyWarnings && conversionOperand is BoundConversion operandConversion && !operandConversion.ConversionKind.IsUserDefinedConversion())
                     {
-                        var explicitType = operandConversion.ConversionGroupOpt.ExplicitType;
-                        if (explicitType.Equals(targetTypeWithNullability, TypeCompareKind.ConsiderEverything))
+                        var explicitType = operandConversion.ConversionGroupOpt?.ExplicitType;
+                        if (explicitType?.Equals(targetTypeWithNullability, TypeCompareKind.ConsiderEverything) == true)
                         {
                             TrackAnalyzedNullabilityThroughConversionGroup(
                                 calculateResultType(targetTypeWithNullability, fromExplicitCast, operandType.State, isSuppressed, targetType),

src/Compilers/CSharp/Test/Semantic/Semantics/NullableReferenceTypesTests.cs

@@ -51485,6 +51485,24 @@ static void Main(object? x)
             comp.VerifyDiagnostics();
         }
 
+        [Fact, WorkItem(41763, "https://github.com/dotnet/roslyn/issues/41763")]
+        public void Conversions_EnumToUnderlyingType_SemanticModel()
+        {
+            var source = @"
+enum E
+{
+    A = 1,
+    B = (int)A
+}";
+            var comp = CreateCompilation(new[] { source }, options: WithNonNullTypesTrue());
+            var tree = comp.SyntaxTrees.Single();
+            var model = comp.GetSemanticModel(tree);
+            comp.VerifyDiagnostics();
+
+            var node = tree.GetRoot().DescendantNodes().OfType<EnumMemberDeclarationSyntax>().ElementAt(1);
+            model.GetSymbolInfo(node.EqualsValue.Value);
+        }
+
         [Fact]
         public void IdentityConversion_LocalDeclaration()
         {