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
for ( int i = 0; i < cellSlot.getCount( ); i++ )
		{
			apply( cellSlot.get( i ) );
			if ( currentElement != null )
			{
				row.addCell( (CellDesign) currentElement );
			}
		}
		currentElement = row;
	}
	/**
	 * Sets up cell element's style attribute.
	 * 
	 * @param cell
	 *            engine's styled cell element.
	 * @param handle
	 *            DE's styled cell element.
	 */
	protected void setupStyledElement( StyledElementDesign design,
			ReportElementHandle handle )
	{
		
		setupReportElement( design, handle );
		StyleDeclaration style = createPrivateStyle( handle );
		if ( style != null && !style.isEmpty( ) )
		{
			design.setStyleName( assignStyleName( style ) );
		}
	}
	public void visitCell( CellHandle handle )