When there are no rows created in the sheet, sheet.getLastRowNum() returns 0 but when there is 1 row created, sheet.getLastRowNum() also returns 0. Shouldn't sheet.getLastRowNum() return -1 for sheet that has no rows?

This is causing issues when you try to create a new row based on the last row number. Due to the above issue, the first row that gets created will start from the 2nd row instead of the very top.

private Row row;

    public void createRow() {
        row = sheet.createRow(sheet.getLastRowNum() + 1);
    }