`Button` can't be converted to `Control`

import QtQuick
import QtQuick.Window
import QtQuick.Controls

ApplicationWindow {
    id: root
    visible: true
    height: 480
    width: 640

    Text {
        anchors.bottom: parent.bottom
        text: "Current focus: " + (root.activeFocusControl as Control)
    }

    Row {
        Repeater {
            model: 16

            Button {
                required property int index

                text: index
            }
        }
    }
}