XLSX JAVA Read file using Hashmap

I was told to use hashmap in this code to allow a XLSX file to be uploaded and be able to be read on the website. The data I key into the XLSX has to be captured on the website too. As for now, there's a null exception error.
This is how my code looks like now.

     OPCPackage pkg = null;
     XSSFWorkbook workbook = null;
     XSSFSheet sheet = null;

    try {
        pkg = OPCPackage.open("C:\\Users\\....Load_AcctCntr_Template.xlsx");
        System.out.println(_LOC + "1.0 " + " pkg:" + pkg);
        workbook = new XSSFWorkbook(pkg);
        System.out.println(_LOC + "1.0 " + " workbook:" + workbook);
        sheet = workbook.getSheetAt(Sheetindex);
        System.out.println(_LOC + "1.0 " + " sheet:" + sheet);
        pkg.close();
    } catch (Exception e) {
        System.out.println(_LOC + "1.0 " + " Test:");
        return _m;
    }   

    System.out.println(_LOC + "1.0 " + " sheet.getRow(0):" + sheet.getRow(0));
    int _totalc = sheet.getRow(0).getLastCellNum();
    int _totalr = sheet.getLastRowNum();


           // Header r=0
           String[] st = new String[_totalc];
           for (int c = 0; c < _totalc; c++) {
              st[c] = sheet.getRow(0).getCell(0).getStringCellValue();

    }

        _m.put("HEADER", st);
        System.out.println(_LOC + "1.0 " + " _m:" + _m);

        // Data r=1 thereafter
        List list = new ArrayList();
        for (int r = 1; r < _totalr; r++) {
            Object[] o = new Object[_totalc];
            String strRow = null;

            for (int c = 0; c < _totalc; c++) {
                o[c] = sheet.getRow(r).getCell(c);
                String cn = o[c].getClass().getName();
                String strCell = null;

                if (!isEmptyNull(strCell)) {
                    strRow = "record_available";
                }
            }

            if ((o != null) && (o.length != 0)) {
                list.add(o);

            }
        }
        _m.put("DATA", list);
        System.out.println(_LOC + "1.0 " + " _m:" + _m);
        return _m;
    }
    return _m;
}

What is shown on my console:

   SystemOut     O [RedirectLogin: requiredRights]1.0/BelsizeWeb/faces/module/entity/en1102.xhtml
   SystemOut     O [RedirectLogin: requiredRights]1.0en1102.xhtml
   SystemOut     O [En1102: doEn1102_command_readfileAction]1.0
   SystemOut     O [PageCodeBase: getConstructJXLList]1.0  pkg:org.apache.poi.openxml4j.opc.ZipPackage@a6742ad
   SystemOut     O [PageCodeBase: getConstructJXLList]1.0  workbook:Name: /xl/workbook.xml - Content Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.main+xml
   SystemOut     O [PageCodeBase: getConstructJXLList]1.0  sheet:Name: /xl/worksheets/sheet1.xml - Content Type: application/vnd.openxmlformats-officedocument.spreadsheetml.worksheet+xml
   SystemOut     O [PageCodeBase: getConstructJXLList]1.0  sheet.getRow(0):<xml-fragment r="1" spans="1:7" x14ac:dyDescent="0.25" xmlns:r="http://schemas.openxmlformats.org/officeDocument/2006/relationships" xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" xmlns:x14ac="http://schemas.microsoft.com/office/spreadsheetml/2009/9/ac" xmlns:main="http://schemas.openxmlformats.org/spreadsheetml/2006/main">

 Caused by: java.lang.NullPointerException
at pagecode.PageCodeBase.getConstructJXLList_xlsx(PageCodeBase.java:6527)
at pagecode.module.entity.En1102.doEn1102_command_readfileAction(En1102.java:166)