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
subItem = createSubFolderItem( topItem, TREE_ITEM_LOGICAL );
		createSubTreeItems( subItem, OPERATORS_LOGICAL, IMAGE_OPERATOR );
	}
	/**
	 * Create native object band.Must set Tree before execution.
	 * 
	 */
	public void createNativeObjectsTree( )
	{
		Assert.isNotNull( tree );
		TreeItem topItem = createTopTreeItem( tree, TREE_ITEM_NATIVE_OBJECTS );
		createObjects( topItem, OBJECTS_TYPE_NATIVE );
	}
	/**
	 * Create parameters band. Must set Tree before execution.
	 * 
	 */
	public void createParamtersTree( )
	{
		Assert.isNotNull( tree );
		TreeItem topItem = createTopTreeItem( tree, TREE_ITEM_PARAMETERS );
		for ( Iterator iterator = SessionHandleAdapter.getInstance( )
				.getReportDesignHandle( )
				.getAllParameters( )
				.iterator( ); iterator.hasNext( ); )
		{
			ReportElementHandle handle = (ReportElementHandle) iterator.next( );
			if ( handle instanceof ParameterHandle )
			{
				createSubTreeItem( topItem,