class ProjectModel : ItemViewModel<Project>() {

    val id = bind(Project::id)
    val companyId = bind(Project::companyId)
    val sender = SenderModel()

    init {
        id.onChange {
            sender.itemProperty.bindBidirectional(SimpleObjectProperty<Sender>(item?.sender))
        }
    }

    override fun onCommit() {
        sender.commit()
        item = Project(
                id.value,
                companyId.value,
                sender.item,
                0.0,
                0.0
        )
    }

}

Oracle is intending to decouple JavaFX from the JDK. We will wait until the decoupled JavaFX is available and stable before upgrading TornadoFX to support it. As of now there is little value and significant effort involved in updating to JDK 9/10, while there will be an enormous value in updating to the decoupled version.