Do not return favorites in expansions of null values

src/ExpressionEvaluator/CSharp/Test/ResultProvider/ObjectFavoritesTests.cs

@@ -81,6 +81,51 @@ class C
                 EvalResult("s2", @"""S2""", "string", "(new C()).a.s2", DkmEvaluationResultFlags.RawString | DkmEvaluationResultFlags.CanFavorite, editableValue: @"""S2"""));
         }
 
+        [Fact]
+        public void ExpansionOfNullValue()
+        {
+            var source =
+@"class A
+{
+    string s1 = ""S1"";
+    string s2 = ""S2"";
+}
+class B
+{
+    A a1 = new A();
+    A a2 = null;
+}";
+
+            var assembly = GetAssembly(source);
+            var type = assembly.GetType("B");
+            var rootExpr = "new B()";
+
+            var favoritesByTypeName = new Dictionary<string, DkmClrObjectFavoritesInfo>()
+            {
+                { "A", new DkmClrObjectFavoritesInfo(new[] { "s2" }) }
+            };
+
+            var runtime = new DkmClrRuntimeInstance(ReflectionUtilities.GetMscorlib(assembly), favoritesByTypeName);
+
+            var value = CreateDkmClrValue(
+                value: Activator.CreateInstance(type),
+                type: runtime.GetType((TypeImpl)type));
+
+            var evalResult = FormatResult(rootExpr, value);
+            Verify(evalResult,
+                EvalResult(rootExpr, "{B}", "B", rootExpr, DkmEvaluationResultFlags.Expandable));
+            var children = GetChildren(evalResult);
+            Verify(children,
+                EvalResult("a1", "{A}", "A", "(new B()).a1", DkmEvaluationResultFlags.Expandable | DkmEvaluationResultFlags.CanFavorite | DkmEvaluationResultFlags.HasFavorites),
+                EvalResult("a2", "null", "A", "(new B()).a2", DkmEvaluationResultFlags.CanFavorite));
+
+            // A a1 = new A();
+            var more = GetChildren(children[0]);
+            Verify(more,
+                EvalResult("s2", @"""S2""", "string", "(new B()).a1.s2", DkmEvaluationResultFlags.RawString | DkmEvaluationResultFlags.CanFavorite | DkmEvaluationResultFlags.IsFavorite, editableValue: @"""S2"""),
+                EvalResult("s1", @"""S1""", "string", "(new B()).a1.s1", DkmEvaluationResultFlags.RawString | DkmEvaluationResultFlags.CanFavorite, editableValue: @"""S1"""));
+        }
+
         [Fact]
         public void FilteredExpansion()
         {

src/ExpressionEvaluator/Core/Source/ResultProvider/Expansion/MemberExpansion.cs

@@ -79,7 +79,7 @@ internal sealed class MemberExpansion : Expansion
 
             foreach (var member in allMembers)
             {
-                if (member.IsFavorite)
+                if (member.IsFavorite && !value.IsNull) // Favorites are never static
                 {
                     favoritesMembersByName.Add(member.Name, member);
                 }

src/ExpressionEvaluator/VisualBasic/Test/ResultProvider/ObjectFavoritesTests.vb

@@ -69,6 +69,49 @@ End Class"
                 EvalResult("s2", """S2""", "String", "(new C()).a.s2", DkmEvaluationResultFlags.RawString Or DkmEvaluationResultFlags.CanFavorite, editableValue:="""S2"""))
         End Sub
 
+        <Fact>
+        Public Sub ExpansionOfNullValue()
+
+            Dim source =
+"Class A
+    Dim s1 As String = ""S1""
+    Dim s2 As String = ""S2""
+End Class
+Class B
+    Dim a1 As A = new A()
+    Dim a2 As A = Nothing
+End Class"
+
+            Dim assembly = GetAssembly(source)
+            Dim type = assembly.GetType("B")
+            Dim rootExpr = "new B()"
+
+            Dim favoritesByTypeName = New Dictionary(Of String, DkmClrObjectFavoritesInfo) From
+            {
+                {"A", New DkmClrObjectFavoritesInfo(New String() {"s2"})}
+            }
+
+            Dim runtime = New DkmClrRuntimeInstance(ReflectionUtilities.GetMscorlib(assembly), favoritesByTypeName)
+
+            Dim value = CreateDkmClrValue(
+                value:=Activator.CreateInstance(type),
+                type:=runtime.GetType(type))
+
+            Dim result = FormatResult(rootExpr, value)
+            Verify(result,
+                EvalResult(rootExpr, "{B}", "B", rootExpr, DkmEvaluationResultFlags.Expandable))
+            Dim children = GetChildren(result)
+            Verify(children,
+                EvalResult("a1", "{A}", "A", "(new B()).a1", DkmEvaluationResultFlags.Expandable Or DkmEvaluationResultFlags.CanFavorite Or DkmEvaluationResultFlags.HasFavorites),
+                EvalResult("a2", "Nothing", "A", "(new B()).a2", DkmEvaluationResultFlags.CanFavorite))
+
+            ' Dim a1 As A = new A()
+            Dim more = GetChildren(children(0))
+            Verify(more,
+                EvalResult("s2", """S2""", "String", "(new B()).a1.s2", DkmEvaluationResultFlags.RawString Or DkmEvaluationResultFlags.CanFavorite Or DkmEvaluationResultFlags.IsFavorite, editableValue:="""S2"""),
+                EvalResult("s1", """S1""", "String", "(new B()).a1.s1", DkmEvaluationResultFlags.RawString Or DkmEvaluationResultFlags.CanFavorite, editableValue:="""S1"""))
+        End Sub
+
         <Fact>
         Public Sub FilteredExpansion()