Grail 3.1 empty list is saving as null in mongodb

[zaid2130]

Hey, I am using grails 3.1. In this version, by default mongo is using MongoCodecSession but I have convertd it to MongoSession for some reason. Now when I am saving my domain instance in mongodb, it is saving empty list as null values which causes problem is $push. Below is my saving code

if(commit){
instance.save(flush: true)
instances.add(instance)
}

Any help?