protected void updatePlus(Item item, Object element) {
		boolean hasPlus = getItemCount(item) > 0;
		boolean needsPlus = isExpandable(item, null, element);
		boolean removeAll = false;
		boolean addDummy = false;
		Object data = item.getData();
		if (data != null && equals(element, data)) {
			// item shows same element
			if (hasPlus != needsPlus) {
				if (needsPlus) {
					addDummy = true;
				} else {
					removeAll = true;
				}
			}
		} else {
			// item shows different element
			removeAll = true;
			addDummy = needsPlus;

			// we cannot maintain expand state so collapse it
			setExpanded(item, false);
		}
		if (removeAll) {
			// remove all children
			Item[] items = getItems(item);
			for (int i = 0; i < items.length; i++) {
				if (items[i].getData() != null) {
					disassociate(items[i]);
				}
				items[i].dispose();
			}
		}
		if (addDummy) {
			newItem(item, SWT.NULL, -1); // append a dummy
		}
	}