AWT Clipboard String handling in Kotlin

Clipboard.kt

fun Clipboard.onChanged(block: (String?) -> Unit) {
    addFlavorListener { e -> block((e.source as Clipboard).clipboardString) }
}

var Clipboard.clipboardString: String?
    set(value) {
        val ss = StringSelection(value)
        setContents(ss, ss)
    }
    get() {
        return try {
            getData(DataFlavor.stringFlavor).toString()
        } catch (e: Exception) {
            null
        }
    }

fun test() {
  val c: Clipboard = Toolkit.getDefaultToolkit().systemClipboard
  val currntCpString = c.clipboardString
  c.onChanged { string ->
    text = string ?: "error: cannot get clipboard"
  }
}

not supporting removeFlavorListener