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
}
	protected SourceViewer getExpressionViewer( )
	{
		return expressionViewer;
	}
	/**
	 * Gets an icon image by the key in plugin.properties
	 * 
	 * @param id
	 * @return image
	 */
	private static Image getIconImage( String id )
	{
		return ReportPlatformUIImages.getImage( id );
	}
	private void createObjects( TreeItem topItem, String objectType )
	{
		for ( Iterator itor = DesignEngine.getMetaDataDictionary( )
				.getClasses( )
				.iterator( ); itor.hasNext( ); )
		{
			IClassInfo classInfo = (IClassInfo) itor.next( );
			if ( classInfo.isNative( )
					&& OBJECTS_TYPE_BIRT.equals( objectType )
					|| !classInfo.isNative( )
					&& OBJECTS_TYPE_NATIVE.equals( objectType ) )
			{
				continue;
			}
			TreeItem subItem = createSubFolderItem( topItem, classInfo );