Cannot serialize Exception as object

[Freeesia]

NEST/Elasticsearch.Net version:
7.4.2
Elasticsearch version:
7.3.1

Description of the problem including expected versus actual behavior:
If I set a class that inherits Exception to the value of Dictionary<string, object> and post it to index, the following InvalidCastException is thrown.

Message: Unable to cast object of type 'Elasticsearch.Net.ExceptionFormatter' to type  'Elasticsearch.Net.Utf8Json.IJsonFormatter`1 [System.NullReferenceException]'.
StackTrace: Elasticsearch.Net.ExceptionFormatterResolver.GetFormatter<T>()
	Elasticsearch.Net.ElasticsearchNetFormatterResolver.InnerResolver.GetFormatter.AnonymousMethod__4_0<T>(System.Type)
	System.Collections.Concurrent.ConcurrentDictionary<TKey, TValue>.GetOrAdd(TKey, System.Func<TKey, TValue>)
	Elasticsearch.Net.ElasticsearchNetFormatterResolver.InnerResolver.GetFormatter<T>()

I hope it can be sent without problems.

Steps to reproduce:
Since it occurs at the time of serializing PostData, i attach the reproduction code

var settings = new ConnectionConfiguration();

var dic = new Dictionary<string, object>()
{
    ["Exception"] = new NullReferenceException(),
};

var data = PostData.Serializable(dic);
using var ms = new MemoryStream();
data.Write(ms, settings); // Exception is thrown!!

[Mpdreamz]

This looks like a bug thanks for reporting, we'll look into this.

[russcam]

Thanks for reporting @Freeesia, I've opened #4378

[Freeesia]

@russcam
Thank you for the fix. I look forward to being released.