Create custom converter for JSON serialization in .NET8 (#717)

* Create custom converter for JSON serialization in .NET8

* Add check for different dictionary type for null replacement

---------

Co-authored-by: Eric Hua <[email protected]>

Src/PChecker/CheckerCore/SystematicTesting/TestingEngine.cs

@@ -97,9 +97,25 @@ public class TestingEngine
         {
             DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
             PropertyNamingPolicy = JsonNamingPolicy.CamelCase,
-            WriteIndented = true
+            WriteIndented = true,
+            Converters = { new EncodingConverter() }
         };
 
+        internal class EncodingConverter : JsonConverter<Encoding>
+        {
+            public override Encoding Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+            {
+                var name = reader.GetString();
+                if (name == null)
+                    return null;
+                return Encoding.GetEncoding(name);
+            }
+            public override void Write(Utf8JsonWriter writer, Encoding value, JsonSerializerOptions options)
+            {
+                writer.WriteStringValue(value.WebName);
+            }
+        }
+
         /// <summary>
         /// The profiler.
         /// </summary>
@@ -618,9 +634,18 @@ public object RecursivelyReplaceNullWithString(object obj) {
             if (obj == null) {
                 return "null";
             }
-            if (obj is Dictionary<string, object> dictionary) {
+            if (obj is Dictionary<string, object> dictionaryStr) {
                 var newDictionary = new Dictionary<string, object>();
-                foreach (var item in dictionary) {
+                foreach (var item in dictionaryStr) {
+                    var newVal = RecursivelyReplaceNullWithString(item.Value);
+                    if (newVal != null)
+                        newDictionary[item.Key] = newVal;
+                }
+                return newDictionary;
+            }
+            else if (obj is Dictionary<int, object> dictionaryInt) {
+                var newDictionary = new Dictionary<int, object>();
+                foreach (var item in dictionaryInt) {
                     var newVal = RecursivelyReplaceNullWithString(item.Value);
                     if (newVal != null)
                         newDictionary[item.Key] = newVal;