Fix Json Merge object

src/OrchardCore/OrchardCore.Abstractions/Json/Nodes/JObject.cs

@@ -98,10 +98,16 @@ public static bool TryParse(string json, out JsonObject? jsonObject, JsonNodeOpt
         {
             if (item.Value is null)
             {
+                if (settings!.MergeNullValueHandling == MergeNullValueHandling.Merge)
+                {
+                    jsonObject[item.Key] = null;
+                }
+
                 continue;
             }
 
             var existingProperty = jsonObject[item.Key];
+
             if (existingProperty is null)
             {
                 jsonObject[item.Key] = item.Value.Clone();
@@ -123,7 +129,7 @@ public static bool TryParse(string json, out JsonObject? jsonObject, JsonNodeOpt
             if (existingProperty is JsonValue || existingProperty.GetValueKind() != item.Value.GetValueKind())
             {
                 if (item.Value.GetValueKind() != JsonValueKind.Null ||
-                    settings?.MergeNullValueHandling == MergeNullValueHandling.Merge)
+                    settings!.MergeNullValueHandling == MergeNullValueHandling.Merge)
                 {
                     jsonObject[item.Key] = item.Value.Clone();
                 }

src/OrchardCore/OrchardCore.ContentManagement.Abstractions/ContentExtensions.cs

@@ -1,5 +1,6 @@
 using System.Text.Json;
 using System.Text.Json.Nodes;
+using System.Text.Json.Serialization;
 using System.Text.Json.Settings;
 
 namespace OrchardCore.ContentManagement;
@@ -17,6 +18,11 @@ public static class ContentExtensions
         MergeNullValueHandling = MergeNullValueHandling.Merge
     };
 
+    private static readonly JsonSerializerOptions _jsonReadExistingObjectSettings = new(JOptions.Default)
+    {
+        DefaultIgnoreCondition = JsonIgnoreCondition.Never,
+    };
+
     /// <summary>
     /// Gets a content element by its name.
     /// </summary>
@@ -186,7 +192,7 @@ public static ContentElement Apply(this ContentElement contentElement, string na
         var elementData = contentElement.Data[name] as JsonObject;
         if (elementData is not null)
         {
-            elementData.Merge(JObject.FromObject(element), _jsonMergeSettings);
+            elementData.Merge(JObject.FromObject(element, _jsonReadExistingObjectSettings), _jsonMergeSettings);
         }
         else
         {

test/OrchardCore.Tests/ContentManagement/ContentElementTests.cs

@@ -66,4 +66,30 @@ public void Get_WhenCastingConcreteTypeThenBaseType_ReturnNewInstance()
         // contentPart should be returned from cache, so it must be same as actualPart.
         Assert.Same(contentPart, actualPart);
     }
+
+    [Theory]
+    [InlineData(15)]
+    [InlineData(-15)]
+    [InlineData(null)]
+    public void Apply_WhenCalledWithNullProperty_SetThePropertyToNull(int? minutes)
+    {
+        // Arrange
+        var contentItem = new ContentItem();
+
+        // Act
+        contentItem.Apply(new TestContentPart()
+        {
+            Minutes = minutes,
+        });
+
+        var part = contentItem.As<TestContentPart>();
+
+        // Assert
+        Assert.Equal(minutes, part.Minutes);
+    }
+}
+
+public class TestContentPart : ContentPart
+{
+    public int? Minutes { get; set; }
 }