using "if" inside a Listbox' template cause an exception

Steps to Reproduce

1. run the zul below

    <zscript><![CDATA[
ListModelList model = new ListModelList();
model.add("item1");
model.add("item2");
model.add("item3");
model.add("best");
]]></zscript>

    <listbox apply="org.zkoss.bind.BindComposer" width="300px" height="600px" model="@load(model)">
        <listhead>
            <listheader label="item"/>
        </listhead>
        <template name="model">
            <if test="@load(each eq 'best')">
                <listitem>
                    <listcell>
                        <button label="test"/>
                    </listcell>
                </listitem>
            </if>
        </template>
    </listbox>

Current Result

SEVERE:
org.zkoss.zk.ui.UiException: The model template must have exactly one item, not 0
at org.zkoss.bind.impl.BindListitemRenderer.render(BindListitemRenderer.java:94)
at org.zkoss.zul.Listbox$Renderer.render(Listbox.java:2769)
at org.zkoss.zul.Listbox.renderItems(Listbox.java:2891)
at org.zkoss.zul.Listbox.service(Listbox.java:3731)
at org.zkoss.zk.ui.impl.DesktopImpl.service(DesktopImpl.java:784)
at org.zkoss.zk.ui.impl.UiEngineImpl.execUpdate(UiEngineImpl.java:1310)
at org.zkoss.zk.au.http.DHtmlUpdateServlet.process(DHtmlUpdateServlet.java:611)

Expected Result

one item rendered

debug info

this bug has a similar problem with ZK-3630