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/TableItemExecutor.java
for ( int i = 0; i < table.getGroupCount( ); i++ )
			{
				TableGroupDesign group = table.getGroup( i );
				if ( group != null && hasDropCellsInGroup( group ) )
				{
					dropCellsInGroup[i] = true;
				} else
				{
					dropCellsInGroup[i] = false;
				}
			}
		}
		/**
		 * scan the row to see if the row has drop cells.
		 * 
		 * @param row
		 *            row design to be tested.
		 * @return true: the row has drop cells. false: no drop cells.
		 */
		private boolean hasDropCellsInRow( RowDesign row )
		{
			for ( int i = 0; i < row.getCellCount( ); i++ )
			{
				CellDesign cell = row.getCell( i );
				String drop = cell.getDrop( );
				if ( drop != null && !"none".equals( drop ) )
				{
					return true;
				}
			}