Not necessarily specify the icon for each item.
_icon = set.getString("icon", "icon.noimage");
If you have not added to the description of an item icon name, the default value is used "icon.noimage".
As a result, use of icons in the properties of scripts much easier.
<img src=" + ItemTable.getInstance().getTemplate(itemId).getIcon() + " height=32 width=32>
Therefore, any other choices are an invention of the bicycle.
Have a nice day!