Finalización de la aplicación debido a la excepción no detectada 'FIRInvalidArgumentException', razón: 'Tipo no admitido: _SwiftValue'

Estoy intentando crear o actualizar un documento en Firestore y obtengo ese error.

 DispatchQueue.main.asyncAfter(deadline: .now() + 0.2, execute: { let docData: [String: Any] = [ "firebase_buyer_id": "222", // todo - set buyer id correctly "firebase_seller_id": "String(describing: self!.ad.ownerId)", "reference_object": [ "reference_object_id": "testing_id", "last_updated_time": Timestamp(date: Date()), "chat_item_list": [ { [ "chat_id": "12", // set chat id "owner_id": "222", "time_stamp": Timestamp(date: Date()), "message": "testing message - hi, message send successfully" ] } ] ] ] self!.db.collection((self?.collectionName)!).document((self?.refId)!).setData(docData){ err in if let err = err { print("Error writing document: \(err)") } else { print("Document successfully written!") } } })