Add tests for "op" Replace with null checks

test/Microsoft.AspNetCore.JsonPatch.Test/NestedObjectTests.cs

@@ -907,6 +907,29 @@ public void Replace()
             Assert.Equal(12, doc.SimpleDTO.DecimalValue);
         }
 
+        [Fact]
+        public void Replace_DTOWithNullCheck()
+        {
+            // Arrange
+            var doc = new SimpleDTOWithNestedDTOWithNullCheck()
+            {
+                SimpleDTOWithNullCheck = new SimpleDTOWithNullCheck()
+                {
+                    StringProperty = "A"
+                }
+            };
+
+            // create patch
+            var patchDoc = new JsonPatchDocument<SimpleDTOWithNestedDTOWithNullCheck>();
+            patchDoc.Replace(o => o.SimpleDTOWithNullCheck.StringProperty, "B");
+
+            // Act
+            patchDoc.ApplyTo(doc);
+
+            // Assert
+            Assert.Equal("B", doc.SimpleDTOWithNullCheck.StringProperty);
+        }
+
         [Fact]
         public void ReplaceWithSerialization()
         {

test/Microsoft.AspNetCore.JsonPatch.Test/ObjectAdapterTests.cs

@@ -648,6 +648,26 @@ public void Replace()
             Assert.Equal(12, doc.DecimalValue);
         }
 
+        [Fact]
+        public void Replace_DTOWithNullCheck()
+        {
+            // Arrange
+            var doc = new SimpleDTOWithNullCheck()
+            {
+                StringProperty = "A",                
+            };
+
+            // create patch
+            var patchDoc = new JsonPatchDocument<SimpleDTOWithNullCheck>();
+            patchDoc.Replace(o => o.StringProperty, "B");
+
+            // Act
+            patchDoc.ApplyTo(doc);
+
+            // Assert
+            Assert.Equal("B", doc.StringProperty);
+        }
+
         [Fact]
         public void ReplaceWithSerialization()
         {

test/Microsoft.AspNetCore.JsonPatch.Test/SimpleDTOWithNestedDTOWithNullCheck.cs

@@ -0,0 +1,15 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace Microsoft.AspNetCore.JsonPatch
+{
+    public class SimpleDTOWithNestedDTOWithNullCheck
+    {
+        public SimpleDTOWithNullCheck SimpleDTOWithNullCheck { get; set; }
+
+        public SimpleDTOWithNestedDTOWithNullCheck()
+        {
+            SimpleDTOWithNullCheck = new SimpleDTOWithNullCheck();
+        }
+    }
+}

test/Microsoft.AspNetCore.JsonPatch.Test/SimpleDTOWithNullCheck.cs

@@ -0,0 +1,29 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+
+namespace Microsoft.AspNetCore.JsonPatch
+{
+    public class SimpleDTOWithNullCheck
+    {
+        string stringProperty;
+
+        public string StringProperty
+        {
+            get
+            {
+                return stringProperty;
+            }
+
+            set
+            {
+                if (value == null)
+                {
+                    throw new ArgumentNullException();
+                }
+                stringProperty = value;
+            }
+        }
+    }
+}