NativeEntry object format incorrect in Grails 3.1.16

I am converting Grails from 3.0 to 3.1, here, in 3.1 nativeEntry is returning as a domain class while in previous version, nativeEntry is returning as BasicDBObject. Also embedded document format is not same in both version. May be I am not using it in a correct way or there is any bug?
Grails 3.1 is using MongoCodecSession and the problem is arising in this, But when I have converted MongoCodecSession to MongoSession, then afterwards when I am saving my instance's empty list field in mongodb was null. I am preferring MongoCodecSession. Any suggestions?
```
def update_val
class_object.class.withNewSession { MongoCodecSession m ->
update_val = m.pendingUpdates.find {
it.key.name == d.class.getName()
}.value[0]nativeEntry.regions[0]."${instance.getDbKey()}"[0]
}
```

Start by reproducing the Grails 3.0-to-3.1 behavior using the shown withNewSession and pendingUpdates code, then inspect MongoCodecSession and the nativeEntry value. Compare the domain-class versus BasicDBObject and embedded-document formats, including how empty list fields are saved; done means the expected format and persistence behavior are consistent or the discrepancy is documented.

Written by the indexing model from the issue text.