code: static OutputStream toXlsxFile(final IDataModel dataModel) {
          ByteArrayOutputStream xlsx = new ByteArrayOutputStream();
          
          try { toWorkbook(dataModel, (Workbook) null).write(xlsx); }
          catch (IOException e) { throw new CalculationEngineException(e); }
          
          return xlsx;
      }
docs: Uses {@link DataModelConverters#toXlsxFile(IDataModel, InputStream)} with null formatting (no formatting).