Bug 135284 [Viewers] API: need to add methods to StructuredViewer to support ViewerComparator
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/StructuredViewer.java
* 
	 * @param elements
	 *            the array to check
	 */
	protected void assertElementsNotNull(Object[] elements) {
		Assert.isNotNull(elements);
		for (int i = 0, n = elements.length; i < n; ++i) {
			Assert.isNotNull(elements[i]);
		}
	}
	/**
	 * Associates the given element with the given widget. Sets the given item's
	 * data to be the element, and maps the element to the item in the element
	 * map (if enabled).
	 * 
	 * @param element
	 *            the element
	 * @param item
	 *            the widget
	 */
	protected void associate(Object element, Item item) {
		Object data = item.getData();
		if (data != element) {
			if (data != null) {
				disassociate(item);
			}
			item.setData(element);
		}