How I can read excel file and set value to null

I want to read a excel file and if there is any data then I want to set it to null then start writing to it. This is what I have for setting excel sheet data to null. I able to write successfully but before write I want to set the value null.

FileOutputStream out = null;

try{
            FileInputStream file = new FileInputStream(new File("/test.xls"));
            HSSFWorkbook oldFile = new HSSFWorkbook(file);
            HSSFSheet sheet = oldFile.getSheetAt(0);
            file.close();

            oldFile.write(null);
            outFile.close();

        } catch(Exception e){
            e.printStackTrace();
        }

One easy solution is to delete and create a sheet:

File destFile = new File("/test.xls");
FileInputStream fileStream = new FileInputStream(destFile);
POIFSFileSystem fsPoi = new POIFSFileSystem(fileStream);

HSSFWorkbook workbook = new HSSFWorkbook(fsPoi);

int index = 0;

HSSFSheet sheet = workbook.getSheet("Setup");
if(sheet != null)   {
    index = workbook.getSheetIndex(sheet);
    workbook.removeSheetAt(index);
}
workbook.createSheet("Setup");
FileOutputStream output = new FileOutputStream(destFile);
workbook.write(output);
output.close();