avalon中ms-for语句中无法嵌入ms-if

Question

    <script>
            var model = avalon.define({
                $id: 'myduplex',
                arr: [{"name":"a"}, {"name":"b"}, {"name":"c"}, {"name":"d"}]
            })
    </script>


<p ms-for="(index,el) in @arr">{{el.name}}
                <div ms-if="el==null">
                    "a"
                </div>
</p>

这里并不能打印 4 个 "a"