title: Error in slick.js: "Uncaught TypeError: Cannot read property 'add' of null"
body: <p>I used slick js for slider view of image.</p>
  
  <p>Here is my code.</p>
  
  <pre><code>&lt;div class="slider_wrap add-remove"&gt;
      &lt;%= f.fields_for :images do |image_form| %&gt;
        &lt;%#= render 'images_fields', :f =&gt; image_form %&gt;
          &lt;div&gt;
            &lt;%= image_tag image_form.object.picture.url,:class=&gt;"drop_down_link even img_prev" %&gt;
          &lt;/div&gt;
          &lt;div class="image_upload_div"&gt;
            &lt;div class="image-upload"&gt;
              &lt;label&gt;
                &lt;i class="fa fa-cloud-upload"&gt;
                  &lt;%= image_form.file_field :picture ,:'data-role'=&gt;"none",:onchange=&gt;"readURL(this);" , :accept =&gt; 'image/jpeg , image/png' %&gt;
                &lt;/i&gt;
              &lt;/label&gt;
            &lt;/div&gt;
          &lt;/div&gt;
      &lt;% end %&gt;
      &lt;%= f.link_to_add "Add a picture", :images ,:id=&gt;"add_pic" ,:class=&gt;"js-add-slide", :style=&gt;"display: none;"%&gt;
  &lt;/div&gt;
  
  &lt;script&gt;
  function silder(){
      slideIndex = 0;
        $('.add-remove').slick({
          slidesToShow: 2,
          slidesToScroll: 2
        });
        $('.js-add-slide').on('click', function() {
          $('.add-remove').slick('slickAdd');
        });
  
        $('.js-remove-slide').on('click', function() {
          $('.add-remove').slick('slickRemove');
        });
  });
  function readURL(input) {
    if (input.files &amp;&amp; input.files[0]) {
      var reader = new FileReader();
      reader.onload = function (e) {
      $('.img_prev').last()
        .attr('src', e.target.result)
      };
  
      reader.readAsDataURL(input.files[0]);
  
      setTimeout(function(){
        $('#add_pic').trigger('click');
        silder();
      }, 100);
    }
  }
  &lt;/script&gt;
  </code></pre>
  
  <p>Now with this code I got slider working, but its not coming proper I am getting error:</p>
  
  <blockquote>
    <p>Uncaught TypeError: Cannot read property 'add' of null</p>
  </blockquote>