问如果不添加空的<ul>标签，导航选项卡将不起作用

EN

<div class="tabbable-line">

    <ul></ul> <!-- IF I do no put this line, tab doesn't work ! Why ? -->

    <ul class="nav nav-tabs " data-tabs="tabs">
        <li class="active">
            <a href="#needsUI" data-toggle="tab" aria-expanded="true"> Needs
                <span class="icon-basket"></span>
            </a>
        </li>
        <li class="">
            <a href="#offerInformationsUI" data-toggle="tab" aria-expanded="false"> Information
                <span class="icon-notebook"></span>
            </a>
        </li>
        <li class="">
            <a href="#customerUI" data-toggle="tab" aria-expanded="false"> Customer
                <span class="icon-user"></span>
            </a>
        </li>
        <li class="">
            <a href="#confirmUI" data-toggle="tab" aria-expanded="false"> Confirm
                <span class="icon-check"></span>
            </a>
        </li>
    </ul>

    <div class="tab-content">


        <div class="tab-pane active" id="needsUI"></div>


        <div class="tab-pane" id="offerInformationsUI"></div>


        <div class="tab-pane" id="customerUI"></div>


        <div class="tab-pane" id="confirmUI"></div>

    </div>

</div>