I've stumbled upon workbook which gives me: Exception in thread "main" java.lang.NullPointerException at org.apache.poi.hssf.model.Sheet.recalcRowGutter(Sheet.java:3001) at org.apache.poi.hssf.model.Sheet.groupRowRange(Sheet.java:2987) at org.apache.poi.hssf.usermodel.HSSFSheet.groupRow(HSSFSheet.java:1369) when I try to create groups in it. It seems to me that generator of this workbook (CR IX) does not emit GutsRecord.
*** This bug has been marked as a duplicate of 43058 ***