Bug 121687 Exception throws when export data in table which inside a grid cell.
Description: Exception throws when export data in table which inside a grid cell. Steps to reproduce: 1. insert a grid. 2. insert one table to one grid cell. 3. insert another table to the other grid cell. 4. export data in two tables. Expected result: Data are exported. Actual result: Exception in: ReportEngineService.getMetaData( )
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/parser/EngineIRVisitor.java
ListBandDesign header = createListBand( handle.getHeader( ) );
		listGroup.setHeader( header );
		ListBandDesign footer = createListBand( handle.getFooter( ) );
		listGroup.setFooter( footer );
		currentElement = listGroup;
	}
	/**
	 * create a table group using the DE's TableGroup.
	 * 
	 * @param handle
	 *            De's table group
	 * @return engine's table group
	 */
	public void visitTableGroup( TableGroupHandle handle )
	{
		TableGroupDesign tableGroup = new TableGroupDesign( );
		setupGroup( tableGroup, handle );
		TableBandDesign header = createTableBand( handle.getHeader( ) );
		tableGroup.setHeader( header );
		TableBandDesign footer = createTableBand( handle.getFooter( ) );
		tableGroup.setFooter( footer );
		currentElement = tableGroup;
	}
	public void visitTextItem( TextItemHandle handle )
	{
		
		TextItemDesign textItem = new TextItemDesign( );
		setupReportItem( textItem, handle );
		String contentType = handle.getContentType( );
		if ( contentType != null )