code: private void handleItemImageRequest(final Request request) {
  
  		// Check for tree item id
  		String itemId = request.getParameter(ITEM_REQUEST_KEY);
  		if (itemId == null) {
  			throw new SystemException("No tree item id provided for image request.");
  		}
  
  		// Check valid item id
  		if (!isValidTreeItem(itemId)) {
  			throw new SystemException("Tree item id for an image request [" + itemId + "] is not valid.");
  		}
  
  		List<Integer> index = getExpandedItemIdIndexMap().get(itemId);
  		TreeItemImage image = getTreeModel().getItemImage(index);
  		if (image == null) {
  			throw new SystemException("Tree item id [" + itemId + "] does not have an image.");
  		}
  
  		ContentEscape escape = new ContentEscape(image.getImage());
  		throw escape;
  	}
docs: Handle a targeted request to retrieve the tree item image.
  
  @param request the request being processed