Nav's selectedItem causes a JS error when the navitem is being invalidated

<zk>
    <label multiline="true">
        1. Please open "Test Selection issue"
        2. Please select "Child 1", it should be selected.
        2. Please select "Child 2", if it cannot be selected that's a bug.
    </label>
<navbar id="navbar" orient="vertical" collapsed="false"
        onSelect="self.getSelectedItem().invalidate()">

    <nav label="Test Selection issue" iconSclass="z-icon-home">
        <navitem label="Child 1"/>
        <navitem label="Child 2"/>
        <navitem label="Child 3"/>
        <navitem label="Child 4"/>
        <navitem label="Child 5"/>
    </nav>
</navbar>
</zk>