Caldroidlistener doesn't work under Kotlin

Question

I'm trying to implement Caldroid in my Software. To check if the user is clicking anything, I am setting up a Listener like this:

val listener = object : CaldroidListener() {
        fun onSelectDate(date: Date, view: View) {
            Toast.makeText(
                applicationContext, formatter.format(date),
                Toast.LENGTH_SHORT
            ).show()
        }

        override fun onChangeMonth(month: Int, year: Int) {
            val text = "month: $month year: $year"
            Toast.makeText(
                applicationContext, text,
                Toast.LENGTH_SHORT
            ).show()
        }

        fun onLongClickDate(date: Date, view: View) {
            Toast.makeText(
                applicationContext,
                "Long click " + formatter.format(date),
                Toast.LENGTH_SHORT
            ).show()
        }

        override fun onCaldroidViewCreated() {
            Toast.makeText(
                applicationContext,
                "Caldroid view is created",
                Toast.LENGTH_SHORT
            ).show()
        }

}

However:Android puts out an error on the "object"-tag, saying: "Object is not abstract and does not implement abstract base class member public abstract fun onSelectDate(date: Date!, view: View!): Unit defined in com.roomorama.caldroid.Caldroidlistener'

Does anyone know how to deal with this?