Bug 135790 ClassCastException in RowData.
ClassCastException is thrown in RowData line 81(IBaseExpression expr = ( IBaseExpression ) valueExpressions.get( index - 1 );).
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/executor/GridItemExecutor.java
*            the executor context
	 * @param visitor
	 *            the report executor visitor
	 */
	public GridItemExecutor( ExecutionContext context,
			IReportItemVisitor visitor )
	{
		super( context, visitor );
	}
	/**
	 * execute a grid. The execution process is:
	 * <li> create a Table content
	 * <li> push it into the stack
	 * <li> execute the query and seek to the first record
	 * <li> process the table style, visiblity, action, bookmark
	 * <li> execute the onCreate if necessary.
	 * <li> call emitter to start the grid.
	 * <li> for each row, execute the row.
	 * <li> call emitter to close the grid.
	 * <li> close the query
	 * <li> popup the table.
	 * 
	 * @see org.eclipse.birt.report.engine.excutor.ReportItemExcutor#excute()
	 */
	public void execute( ReportItemDesign item, IContentEmitter emitter )
	{
		GridItemDesign gridItem = ( GridItemDesign ) item;
		ITableContent tableObj = report.createTableContent( );
		IContent parent = context.getContent( );
		context.pushContent( tableObj );