V4 debugger always assigns ref:0 to undefined values

import QtQuick 2.4
import QtQuick.Window 2.2

Window {
    visible: true
    Rectangle {
        anchors.fill: parent
        property alias mouseArea: mouseArea

        width: 360
        height: 360

        MouseArea {
            function blah(a) {
                console.log("z");
                if (a) {
                    a = a + 12;
                    throw "horstix";
                }
                var b = { a: "a" };
                return b;
            }

            id: mouseArea
            anchors.fill: parent
            onClicked: { var b  = { "employees":[
                                  {"firstName":"John", "lastName":"Doe"},
                                  {"firstName":"Anna", "lastName":"Smith"},
                                  {"firstName":"Peter", "lastName":"Jones"}
                              ] }
                var c = blah(false).a;
                var number = 1;
                var y = {
                    num: 1,
                    fun : function() {return 4; },
                    und : undefined,
                    nul : null,
                    str : "strsta",
                    boo : true,
                    obj : {x: "2"},
                    arr : [1, 1, 1]
                }
                console.log("a");

                var x = {a: 12, b: [1,2,3]};
                Qt.quit();
            }
        }
    }
}