SpreadJS: Create List Validator from Array including empty option

getValidatorFromArray.js

export const getListValidatorFromArray = (spread: GC.Spread.Sheets.Workbook, data: any[]) => {
  // saving validation list values in a hidden sheet
  spread.addSheet(spread.getSheetCount());
  const sheet = spread.getSheet(spread.getSheetCount() - 1);
  sheet.visible(false);
  for (let i = 0; i < data.length; i++) {
    sheet.setValue(i, 0, data[i]);
  }
  // create validator based on the values
  const dv = GC.Spread.Sheets.DataValidation.createFormulaListValidator(
    '=' + sheet.name() + '!$A$1:' + sheet.name() + '!$A$' + data.length
  );
  return dv;
};

Full story: https://stackoverflow.com/q/56040022/5866637

Note: This creates an extra sheet for each validator you create. Makes sure you reuse them as much as possible (i.e. assigning it to a variable when it's created, and reusing the variable for other columns/rows that use the same one).