Listgroup1.addItem = Icon not showing

Hi, I have an empty Listgroup in my project, which I add items later with:

 Listgroup2.addItem( + "<div width=100%><span class=fileDate ><small>" + "Date" + "</small></span></div>");

In the properties window for the Listgroup > Icons I have entered “file” but when I run the programme the icon is missing, when I run it in the browser I can see that the icon is “oi-undefinded”

<span class="oi oi-undefined form-control-feedback" aria-hidden="true"></span>

I have also tried to manually add the icon within my .additem function but get the same result. I have also tried it with different icons but again get the same result. Icons in other areas of the app are all showing ok.

Can you put together a small project with only one Listgroup that demonstrates the issue?

I ended up just implementing a workaround with the following:

.oi-undefined  {
 background: url('images/PDF.png');
 width: 24px;
 height: 24px;
 display: block;