datetimepicker怎么设置空值（浅谈amaze-ui中datepicker和datetimepicker注意的几点）

<li class="inputItem">
    <li class="inputName">制卡时间</li>
     <input type="text" id="gender" name="gender" class="am-form-field data-input" readonly required placeholder="请选择">
 </li>
 <li class="inputItem">
     <li class="inputName">生效时间</li>
     <input type="text" id="startDate" name="startDate" class="am-form-field data-input" readonly required placeholder="请选择">
 </li>
 <li class="inputItem">
     <li class="inputName">过期时间</li>
     <input type="text" id="expDate" name="expDate" class="am-form-field data-input" readonly required placeholder="请选择">
 </li>

initDatePicker = function () {
   //日期插件初始化
   $('#gender').datetimepicker({
       language: 'zh-CN',
       format: 'yyyy-mm-dd hh:ii:ss',
       minView: 2
       //pickerPosition: "bottom-left"
   }).on("changeDate", function (ev) {  //值改变事件
       if (ev.date) {
           $("#startDate").datetimepicker('setStartDate', new Date(ev.date.valueOf()));
       } else {
           $("#startDate").datetimepicker('setStartDate', null);
       }
   });
   $('#startDate').datetimepicker({
       language: 'zh-CN',
       format: 'yyyy-mm-dd hh:ii:ss',
       minView: 2
       //pickerPosition: "bottom-left"
   }).on("changeDate", function (ev) {
       if (ev.date) {
           $("#gender").datetimepicker('setEndDate', new Date(ev.date.valueOf()));
       } else {
           $("#gender").datetimepicker('setEndDate', new Date());
       }
   });
   $('#gender,#startDate').click(function () {
       $(this).datetimepicker("show");
   })
};
initDatePicker1 = function () {
    $('#startDate').datetimepicker({
        language: 'zh-CN',
        format: 'yyyy-mm-dd hh:ii:ss',
        minView: 2
        //pickerPosition: "bottom-left"
    }).on("changeDate", function (ev) {
        if (ev.date) {
            $("#expDate").datetimepicker('setStartDate', new Date(ev.date.valueOf()));
        } else {
            $("#expDate").datetimepicker('setStartDate', new Date());
        }
    });
    $('#expDate').datetimepicker({
        language: 'zh-CN',
        format: 'yyyy-mm-dd hh:ii:ss',
        minView: 2
        //pickerPosition: "bottom-left"
    }).on("changeDate", function (ev) {
        if (ev.date) {
            $("#startDate").datetimepicker('setEndDate', new Date(ev.date.valueOf()));
        } else {
            $("#startDate").datetimepicker('setEndDate', null);
        }
    });
    $('#startDate,#expDate').click(function () {
        $(this).datetimepicker("show");
    })
}