Null value received in a custom formatter for Exception

Bug description

When trying to serialize/deserialize an exception object using TypelessContractlessStandardResolver, some details like StackTrace and Source are getting lost on the deserialized object.
Hence, I tried to write a custom IMessagePackFormatter. There are two scenarios now :

1. Serialize an exception with no inner exception

   The value parameter received in Serialize method is always null

2. Serialize an exception with inner exception

   The value parameter received in Serialize method is the inner exception and not the actual exception that was passed for serialization

As a result, I am not able to get a workaround even with a custom IMessagePackFormatter.

Repro steps

• Add a custom IMessagePackFormatter

  internal class ExceptionFormatter : IMessagePackFormatter<Exception>
 {
    public Exception Deserialize(ref MessagePackReader reader, MessagePackSerializerOptions options)
    {

    }

    public void Serialize(ref MessagePackWriter writer, Exception value, MessagePackSerializerOptions options)
    {
        /// value is null here if exception has no inner exception else inner exception instead of actual exception passed for serialization
    }
 }

• Configure a custom resolver to use the custom ExceptionFormatter

interface ISerializer
{
    byte[] Serialize(object obj);

    T Deserialize<T>(byte[] bytes);
}

public class MessagePackTypeLessSerializer : ISerializer
{
    private static MessagePackSerializerOptions serializerOptions;
    static MessagePackTypeLessSerializer()
    {
        var resolver = CompositeResolver.Create(
               [new ExceptionFormatter()],
               [TypelessContractlessStandardResolver.Instance]);
        serializerOptions = MessagePackSerializerOptions.Standard.WithResolver(resolver); ;
    }

    public byte[] Serialize(object obj)
    {      
        return MessagePackSerializer.Typeless.Serialize(obj, serializerOptions);
    }

    public T Deserialize<T>(byte[] bytes)
    {
        if (MessagePackSerializer.Typeless.Deserialize(bytes, serializerOptions) is T result)
        {
            return result;
        }
        throw new ArgumentException($"Deserialized object is not of type {typeof(T)}");
    }

}

• Throw an exception and try to serialize

ISerializer serializer = new MessagePackContractLessSerializer();
var exception = GetException();
var exceptionSerialized = serializer.Serialize(exception);

Exception GetException()
{
    try
    {
        throw new InvalidOperationException("Invalid Operation");
        //throw new InvalidOperationException("Invalid Operation", new ArgumentException("Inner Exception"));
    }
    catch (Exception ex)
    {
        return ex;
    }   
}

Expected behavior

Correct exception object should be received in Serialize method of the IMessagePackFormatter that was passed for serialization.

Actual behavior

null/inner exception object is received in Serialize method of the IMessagePackFormatter instead of actual exception passed for serialization.

Version used:

.Net Core 8.0 , MessagePack 2.5.172 : Broken
.Net Framework 4.7, MessagePack 2.5.172 : Partly broken (When no inner exception, we get the correct value. Same as .net core when there is inner exception)

首先，使用 issue 中展示的 TypelessContractlessStandardResolver 和 MessagePackSerializerOptions 重現自訂 IMessagePackFormatter 情境，並比較 .NET Core 8.0 與 .NET Framework 4.7 的行為。追蹤 typeless 序列化和 resolver 路徑，以判斷為什麼 Serialize 會收到 null 或內部例外；當 formatter 在兩種情況下都收到原始 Exception 物件時，即表示完成。