const wb = new ExcelJS.Workbook();
wb.csv.read(Stream.Readable.from('firstValue;    ;secondValue', { parserOptions: { delimiter: ';' } })
const ws = wb.worksheets[templateInfo.worksheet];

const row1 = ws.getRow(1);
const cell12 = row1.getCell(2);
console.log('cell: 1,2: ', cell12.value); // 0 => Expected string : '    '

// csv.js
 function(datum) {
    if (datum === '') {
      return null;
    }
    const datumNumber = Number(datum); // -------> Here !!!
    if (!Number.isNaN(datumNumber) && datumNumber !== Infinity) {
      return datumNumber;
    }
    const dt = dateFormats.reduce((matchingDate, currentDateFormat) => {
      if (matchingDate) {
        return matchingDate;
      }
      const dayjsObj = dayjs(datum, currentDateFormat, true);
      if (dayjsObj.isValid()) {
        return dayjsObj;
      }
      return null;
    }, null);
    if (dt) {
      return new Date(dt.valueOf());
    }
    const special = SpecialValues[datum];
    if (special !== undefined) {
      return special;
    }
    return datum;
  };

wb.csv.read(Stream.Readable.from(myCsv, { map: myOwnMapper, parserOptions: { delimiter: ';' } })