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
if ( currentElement != null )
			{
				listItem.addGroup( (ListGroupDesign) currentElement );
			}
		}
		
		SlotHandle detailSlot = handle.getDetail( );
		listItem.setDetail( createListBand( detailSlot ) );
		
		SlotHandle footerSlot = handle.getFooter( );
		listItem.setFooter( createListBand( footerSlot ) );
		currentElement = listItem;
	}
	public void visitFreeForm( FreeFormHandle handle )
	{
		
		FreeFormItemDesign container = new FreeFormItemDesign( );
		setupReportItem( container, handle );
		
		SlotHandle slot = handle.getReportItems( );
		for ( int i = 0; i < slot.getCount( ); i++ )
		{
			apply( slot.get( i ) );
			if ( currentElement != null )
			{
				container.addItem( (ReportItemDesign) currentElement );
			}
		}
		currentElement = container;
	}