Use named argument syntax for null values in json serialization methods

src/System.Text.Json/src/System/Text/Json/Serialization/JsonClassInfo.cs

@@ -435,7 +435,7 @@ public static ulong GetKey(ReadOnlySpan<byte> propertyName)
         public static Type GetElementType(Type propertyType, Type parentType, MemberInfo memberInfo, JsonSerializerOptions options)
         {
             // We want to handle as the implemented collection type, if applicable.
-            Type implementedType = GetImplementedCollectionType(parentType, propertyType, null, out _, options);
+            Type implementedType = GetImplementedCollectionType(parentType, propertyType, propertyInfo: null, out _, options);
 
             if (!typeof(IEnumerable).IsAssignableFrom(implementedType))
             {
@@ -484,7 +484,7 @@ public static ClassType GetClassType(Type type, JsonSerializerOptions options)
             Debug.Assert(type != null);
 
             // We want to handle as the implemented collection type, if applicable.
-            Type implementedType = GetImplementedCollectionType(typeof(object), type, null, out _, options);
+            Type implementedType = GetImplementedCollectionType(typeof(object), type, propertyInfo: null, out _, options);
 
             if (implementedType.IsGenericType && implementedType.GetGenericTypeDefinition() == typeof(Nullable<>))
             {

src/System.Text.Json/src/System/Text/Json/Serialization/JsonSerializerOptions.cs

@@ -355,7 +355,14 @@ internal JsonPropertyInfo GetJsonPropertyInfoFromClassInfo(Type objectType, Json
         {
             if (!_objectJsonProperties.TryGetValue(objectType, out JsonPropertyInfo propertyInfo))
             {
-                propertyInfo = JsonClassInfo.CreateProperty(objectType, objectType, objectType, null, typeof(object), null, options);
+                propertyInfo = JsonClassInfo.CreateProperty(
+                    objectType,
+                    objectType,
+                    objectType,
+                    propertyInfo: null,
+                    typeof(object),
+                    converter: null,
+                    options);
                 _objectJsonProperties[objectType] = propertyInfo;
             }