Describe IncludePublicFields as a fallback and write a shadowed field once

tests/NLog.UnitTests/Targets/DefaultJsonSerializerClassTests.cs

@@ -95,6 +95,16 @@ namespace NLog.UnitTests.Targets
             public string ReadPrivate() => _private;
         }
 
+        private class ClassWithBaseField
+        {
+            public string Name = "base";
+        }
+
+        private sealed class ClassWithShadowingField : ClassWithBaseField
+        {
+            public new string Name = "derived";
+        }
+
         private static ContainerClass BuildSampleObject()
         {
             var testObject = new ContainerClass
@@ -236,6 +246,12 @@ namespace NLog.UnitTests.Targets
             Assert.Equal(@"{""Name"":""John"",""Age"":42}", withFieldsAgain.ToString());
         }
 
+        [Fact]
+        public void IncludePublicFields_ShadowedField_IsWrittenOnce()
+        {
+            Assert.Equal(@"{""Name"":""derived""}", SerializeWithFields(new ClassWithShadowingField()));
+        }
+
         [Fact]
         public void IncludePublicFields_ExpandoObject_StillEnumeratesEntries()
         {