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
}
	/**
	 * execute a cell. the execution process is:
	 * <li> create a cell content
	 * <li> push the content into the stack
	 * <li> intialize the cell
	 * <li> process the action, bookmark, style, visibility
	 * <li> call onCreate if necessary
	 * <li> call emitter to start the cell
	 * <li> for each element in the cell, execute the element.
	 * <li> call emiter to close the cell
	 * <li> popup the cell.
	 * 
	 * @param rowContent
	 *            row content
	 * @param cell
	 *            cell design
	 * @param emitter
	 *            output emitter
	 */
	private void executeCell( IRowContent rowContent, CellDesign cell,
			IContentEmitter emitter, IRowData rowData )
	{
		ICellContent cellContent = report.createCellContent( );
		assert ( cellContent instanceof CellContent );
		context.pushContent( cellContent );
		initializeContent( rowContent, cell, cellContent );
		cellContent.setColumn( cell.getColumn( ) );
		cellContent.setColSpan( cell.getColSpan( ) );
		cellContent.setRowSpan( cell.getRowSpan( ) );