光滑的滑块拇指没有显示

Question

我有一个光滑的滑块，缩略图作为点导航，但拇指出现未定义。这是我的代码。任何帮助是极大的赞赏！

<section class="slider">
<div data-thumb="images/3white.svg?$staticlink$"><img src="images/cutaway3.png?$staticlink$"></div>
<div data-thumb="images/4white.svg?$staticlink$"><img src="images/cutaway4.png?$staticlink$"></div>
<div data-thumb="images/5white.svg?$staticlink$"><img src="images/cutaway5.png?$staticlink$"></div>
<div data-thumb="images/6white.svg?$staticlink$"><img src="images/cutaway6.png?$staticlink$"></div>
<div data-thumb="images/7white.svg?$staticlink$"><img src="images/cutaway7.png?$staticlink$"></div>
<div data-thumb="images/8gray.svg?$staticlink$"><img src="images/cutaway8.png?$staticlink$"></div>
<div data-thumb="images/9gray.svg?$staticlink$"><img src="images/cutaway9.png?$staticlink$"></div>
<div data-thumb="images/Pgray.svg?$staticlink$"><img src="images/cutawayP.png?$staticlink$"></div>
</section>

<script type="text/javascript">
$(".slider").slick({

autoplay: false,
dots: true,
customPaging : function(slider, i) {
    var thumb = $(slider.$slides[i]).data('thumb');
    return '<a><img src="'+thumb+'"></a>';
},

responsive: [{ 
    breakpoint: 500,
    settings: {
        dots: false,
        arrows: false,
        infinite: false,
        slidesToShow: 2,
        slidesToScroll: 2
    } 
}]
});