-Fixed merging null string values

Src/Newtonsoft.Json.Tests/Linq/MergeTests.cs

@@ -46,6 +46,16 @@ namespace Newtonsoft.Json.Tests.Linq
     [TestFixture]
     public class MergeTests : TestFixtureBase
     {
+        [Test]
+        public void MergeNullString()
+        {
+            var a = new JObject { ["a"] = 1 };
+            var b = new JObject { ["a"] = false ? "2" : null };
+            a.Merge(b);
+
+            Assert.AreEqual(1, (int)a["a"]);
+        }
+
         [Test]
         public void MergeObjectProperty()
         {

Src/Newtonsoft.Json/Linq/JObject.cs

@@ -185,7 +185,7 @@ namespace Newtonsoft.Json.Linq
                 {
                     if (!(existingProperty.Value is JContainer existingContainer) || existingContainer.Type != contentItem.Value.Type)
                     {
-                        if (contentItem.Value.Type != JTokenType.Null || settings?.MergeNullValueHandling == MergeNullValueHandling.Merge)
+                        if (!IsNull(contentItem.Value) || settings?.MergeNullValueHandling == MergeNullValueHandling.Merge)
                         {
                             existingProperty.Value = contentItem.Value;
                         }
@@ -198,6 +198,21 @@ namespace Newtonsoft.Json.Linq
             }
         }
 
+        private static bool IsNull(JToken token)
+        {
+            if (token.Type == JTokenType.Null)
+            {
+                return true;
+            }
+
+            if (token is JValue v && v.Value == null)
+            {
+                return true;
+            }
+
+            return false;
+        }
+
         internal void InternalPropertyChanged(JProperty childProperty)
         {
             OnPropertyChanged(childProperty.Name);