Created attachment 32259 [details]
removeMergedRegion tested excel

removeMergedRegion() throws an IndexOutOfBoundsException on .xlsx file. But is working on .xls file

Here I have pasted the tested the code 

void removeRow(Sheet sheet){
    if(sheet){
        for(i in sheet.getFirstRowNum()..sheet.getLastRowNum()){
            Row row = sheet.getRow(i)
            if(!row){
                continue
            }
            for(j in row.getFirstCellNum()..row.getLastCellNum()){
                if(j<0){
                    continue
                }
                sheet.removeMergedRegion(j)
            }
            sheet.removeMergedRegion(i)
            sheet.removeRow(row)
        }
    }
}