Bug 147687 Assert err happened with design ui
Run BIRT in workbench with argument -ea. Assert err happened when using design ui to open a design file.
UI/org.eclipse.birt.report.designer.ui/src/org/eclipse/birt/report/designer/internal/ui/dialogs/ExpressionTreeSupport.java
}
	/**
	 * Creates birt object tree. Must set Tree before execution.
	 * 
	 */
	public void createBirtObjectsTree( )
	{
		Assert.isNotNull( tree );
		TreeItem topItem = createTopTreeItem( tree, TREE_ITEM_BIRT_OBJECTS );
		createObjects( topItem, OBJECTS_TYPE_BIRT );
	}
	/**
	 * Creates a top tree item
	 * 
	 * @param parent
	 * @param text
	 * @return tree item
	 */
	private TreeItem createTopTreeItem( Tree parent, String text )
	{
		TreeItem item = new TreeItem( parent, SWT.NONE );
		item.setText( text );
		item.setImage( IMAGE_FOLDER );
		item.setData( ITEM_DATA_KEY_TOOLTIP, "" );
		return item;
	}
	private TreeItem createSubTreeItem( TreeItem parent, String text,
			Image image, boolean isEnabled )
	{
		return createSubTreeItem( parent, text, image, null, text, isEnabled );