NativeEntry object format incorrect in Grails 3.1.16

[zaid2130]

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]
            }