firestore android adding "stability" field in custom Parcelable class while saving

I have a parcelable class Image

@Parcelize
data class Image(val id:String="",val url:String=""):Parcelable

and for saving in firestore

val data = HashMap<String,Any>()
data["title"] = "My Title"
data["image] = Image("dgdg1","https://someimagepath")
firestore.collection("collectionname").document(documentId).set(data,SetOptions.merge()).await()

data is getting saved in firestore but inside the "image" it is adding an extra field "stability" . The out put result is like this

{  
  "title":"My Title",  
  "image":{
    "stability":0,
    "id":"dgdg1",
    "url":"https://someimagepath"
  } 
}

why is this "stability" is automatically added to the image object.

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