sg.setGroupType("Text");
sg.setGroupType(DataType.TEXT_LITERAL);
    public static final SeriesGrouping create()    {        final SeriesGrouping sg = DataFactory.eINSTANCE.createSeriesGrouping();        sg.setAggregateExpression("Sum");        sg.setGroupingInterval(2);        sg.setEnabled(false);        sg.setGroupType("Text");        return sg;    }