无法将值插入现有工作簿[apache poi]

Question

我想在现有工作簿中插入值。这里封装了这个逻辑的类：

public class FormulaExtractor {
private String pathToExcelFile;
private XSSFWorkbook workbook;
private Map<Double, Formula> idFormular = new HashMap<>();

public FormulaExtractor(String pathToExcelFile) {
    this.pathToExcelFile = pathToExcelFile;
    try (FileInputStream fileInputStream = new FileInputStream(new File(pathToExcelFile))) {
        this.workbook = new XSSFWorkbook(fileInputStream);
    } catch (FileNotFoundException e) {
        System.out.println("Cannot locate a xls file. Exception: " + e.toString());
    } catch (IOException e) {
        System.out.println("IO exception " + e.toString());
    }
}

public void insertHumanReadableFormulas() throws IOException {
    XSSFSheet sheet = workbook.getSheetAt(0);

    Iterator<Row> rowIterator = sheet.iterator();
    while (rowIterator.hasNext()) {
        Row currentRow = rowIterator.next();
        Cell cell = currentRow.createCell(CellReference.convertColStringToIndex("K"));
        cell.setCellValue("Some dummy variable to test. ");
    }

FileOutputStream fileOut = new FileOutputStream(new File(this.pathToExcelFile));
    workbook.write(fileOut);
    fileOut.close();
}

}

我如何使用它：

public class App {
public static void main(String[] args) throws IOException {
    final String pathToExcel = "some/path/some_excel.xlsx";
    FormulaExtractor formulaExtractor = new FormulaExtractor(pathToExcel);

    formulaExtractor.insertHumanReadableFormulas();
    }
}

我没有任何异常或错误。当我打开我的Excel文件时，我根本找不到列“K”中的值。我做错了什么？