Lazy load not adding link to background-image

Question

I have this code in html:

echo '<div class="sponsors__item-bg-img lazy-load" data-original="'.$sponsor_item['image'].'" style="background-image: url();" src="https://static.questex.asia/template7/images/grey.gif" ></div></a>';

And the jquery.lazyload.js got this part:

$self.one("appear", function() {
            if (!this.loaded) {
                if (settings.appear) {
                    var elements_left = elements.length;
                    settings.appear.call(self, elements_left, settings);
                }
                $("<img />")
                    .bind("load", function() {

                        var original = $self.attr("data-" + settings.data_attribute);
                        $self.hide();
                        if ($self.is("img")) {
                            $self.attr("src", original);
                        } else {
                            $self.css("background-image", "url('" + original + "')");
                        }
                        $self[settings.effect](settings.effect_speed);

                        self.loaded = true;

                        /* Remove image from array so it is not looped next time. */
                        var temp = $.grep(elements, function(element) {
                            return !element.loaded;
                        });
                        elements = $(temp);

                        if (settings.load) {
                            var elements_left = elements.length;
                            settings.load.call(self, elements_left, settings);
                        }
                    })
                    .attr("src", $self.attr("data-" + settings.data_attribute));
            }
        });

However, the final result is the image is not loaded, because the url is not added by the js:

<div class="sponsors__item-bg-img lazy-load" data-original="https://img.questex.asia/sites/default/files/styles/219x164/public/BizProLogo.jpg?itok=KLf9ojX0&amp;timestamp=1527822985" style="background-image: url();" src="https://static.questex.asia/template7/images/grey.gif"></div>

Anyone know how can i check what happened or how should i resolve the problem? Thanks.