Bug 221768 [Viewers] Fix for bug 210747 causes NPE when parent is TreePath.EMPTY
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/AbstractTreeViewer.java
* Fires a tree collapsed event. Only listeners registered at the time this
	 * method is called are notified.
	 *
	 * @param event
	 *            the tree expansion event
	 * @see ITreeViewerListener#treeCollapsed
	 */
	protected void fireTreeCollapsed(final TreeExpansionEvent event) {
		Object[] listeners = treeListeners.getListeners();
		boolean oldBusy = isBusy();
		setBusy(true);
		try {
			for (int i = 0; i < listeners.length; ++i) {
				final ITreeViewerListener l = (ITreeViewerListener) listeners[i];
				SafeRunnable.run(new SafeRunnable() {
					public void run() {
						l.treeCollapsed(event);
					}
				});
			}
		} finally {
			setBusy(oldBusy);
		}
	}
	/**
	 * Fires a tree expanded event. Only listeners registered at the time this
	 * method is called are notified.
	 *
	 * @param event
	 *            the tree expansion event