isMarital = $('[name="isMarital"]:checked').val();

 isMarital == null    //当radio选择为空的时候 isMarital 为null

 　　　　<div class="zktit">是否已婚 ：</div>

               <div  class="foru fl">

                   <input type="radio" name="isMarital" value=""/>

                   <label>已婚</label>

               </div>

                <div  class="foru fl">

                   <input type="radio" name="isMarital" value=""/>

                   <label>未婚</label>

               </div>