Transform nested data class to single level Map in Kotlin

Question

Basically I have a data class like

data class House(
  val bedroom: Bedroom,
  val livingroom: Livingroom
)

data class Bedroom(
  val bed: String,
  val pillows: List<String>
)

data class Livingroom(
  val sofa: String,
  val tv: String
)

I wonder how to map the House data model to a map with only one level:

{
   bed = "some-bed",
   pillows = ["pillow-a", "pillow-b", "pillow-c"],
   sofa = "some-sofa",
   tv = "some-tv"
}

I tried gson by first transforming it to a json then to map, but it will give me nested maps