Using the exhibit_builder_thumbnail_gallery filter


I wonder how I can use or change the html of this filter.
I have some items of type video where is there is not image attach to the item. When I attach the item to any of the Exhibit builder layout that use thumbnail gallery function, I saw an empty bracket <div class="exhibit-item"> added to the html even though the item has not image. This problem specifically for items of type video. In 1.5 I did not experience this problem bc this bracket was not added to the html when there is no image, but it is available with Omeka 2.1.1
My question how can I get rid of this bracket?