QML ListModel converts null into 0

var list = [0, null, 1];

append({ value : list[0]});
append({ value : list[1]});
append({ value : list[2]});

import QtQuick 2.7
import QtQuick.Controls 2.0
import QtQuick.Layouts 1.1

ApplicationWindow {
    visible: true
    width: 640
    height: 480

    Pane {

        ListModel {
            id: listModel
            Component.onCompleted: {

                var list = [0, null, 1];

                console.log(list[0]);
                console.log(list[1]); // outputs null
                console.log(list[2]);

                console.log("---");

                append({ value : list[0]});
                append({ value : list[1]});
                append({ value : list[2]});

                console.log(get(0).value);
                console.log(get(1).value); // outputs 0, not null !!!
                console.log(get(2).value);
            }
        }

        Column {
            Repeater {
                model: listModel

                Text {
                    text: model.value === null ? "?" : model.value // question mark is not displayed
                }
            }
        }
    }
}

qml: 0
qml: null
qml: 1
qml: ---
qml: 0
qml: 0
qml: 1