迭代div name取不到next 的值

 <table class="table table-bordered" style="width:100%;">
        <tbody id='tab2' class='table table-hover'><tr><th>序号</th><th>支付时间</th><th>支付金额</th><th>是否已出账</th></tr>
        <tr>
            <td>1</td>
            <td ><div id="rtime1" class="datepicker-target">2014-05-01</div></td>
            <td><input type="text" name="money"/> </td>
            <td>否</td>
        </tr>
        <tr>
            <td>2</td>
            <td><div id='rtime2' class="datepicker-target">2014-05-02</div></td>
            <td><input type="text" name="money"/></td>
            <td>否</td>
        </tr>
        <tr>
            <td>3</td>
            <td><div id='rtime3' class="datepicker-target">2014-05-03</div></td>
            <td><input type="text" name="money"/></td>
            <td>否</td>
        </tr>
        <tr>
            <td>4</td>
            <td><div id='rtime4' class="datepicker-target">2014-05-04</div></td>
            <td><input type="text" name="money"/></td>
            <td>否</td>
        </tr>
        <tr>
            <td>5</td>
            <td><div id='rtime5' class="datepicker-target">2014-05-05</div></td>
            <td><input type="text" name="money"/></td>
            <td>否</td>
        </tr>

        <tr>
            <td>6</td>
            <td><div id='rtime6' class="datepicker-target">2014-05-06</div></td>
            <td><input type="text" name="money"/></td>
            <td>否</td>
        </tr>
        <tr>
            <td>7</td>
            <td><div id='rtime7' class="datepicker-target">2014-05-07</div></td>
            <td><input type="text" name="money"/></td>
            <td>否</td>
        </tr>
        <tr>
            <td>8</td>
            <td><div id='rtime8' class="datepicker-target">2014-05-08</div></td>
            <td><input type="text" name="money"/></td>
            <td>否</td>
        </tr>
        <tr>
            <td>9</td>
            <td><div id='rtime9' class="datepicker-target">2014-05-19</div></td>
            <td><input type="text" name="money"/></td>
            <td>否</td>
        </tr>
        <tr>
            <td>10</td>
            <td><div id='rtime10' class="datepicker-target">2014-05-10</div></td>
            <td><input type="text" name="money"/></td>
            <td>否</td>
        </tr>
        <tr>
            <td>11</td>
            <td><div id='rtime11' class="datepicker-target">2014-05-11</div></td>
            <td><input type="text" name="money"/></td>
            <td>否</td>
        </tr>
        <tr>
            <td>12</td>
            <td><div id='rtime12' class="datepicker-target">2014-05-12</div></td>
            <td><input type="text" name="money"/></td>
            <td>否</td>
        </tr>
        <tr>
            <td colspan="5" style="text-align: center" >
            <button type="button" class="btn" id="okBtn">
                <span>保存</span>
            </button>
            <button type="button" class="btn" id="backBtn">
                <span>返回</span>
            </button>
        </td></tr>
        </tbody>
    </table>

<script>
$(function(){
    $(".datepicker-target").each(function(){
        var value=$(this).html();
            var next=$(this).next().html();
             if(next!=null){
                 if(value>next){
                     alert("前面的时间大于后面的时间");
                     return; 
                 }
             }
        
    });

 为什么next的值是null，怎么获取next的值？