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kotlinlang

I have a weird behavior here with Spring Boot MongoDb. This document:
```
@Document(collection = "schedules")
data class ScheduleDocument(val payload: Payload) {
}
```
is stored as:
```
{
    "_id" : ObjectId("5a636f2e5017622fc0c4654a"),
    "_class" : "example.Payload",
    "channel" : "push",
    "schedule" : ISODate("2018-01-20T16:32:46.535Z")
}
```
But I was expecting `payload` to be a subdocument, like this:
```
{
	"_id" : ObjectId("5a636f2e5017622fc0c4654a"),
	"_class" : "example.ScheduleDocument",
	"payload": {
	    "channel" : "push",
	    "schedule" : ISODate("2018-01-20T16:32:46.535Z")
	}
}
```
can anyone explain this behavior?