protected function getDateTimes(array $parameters, $format) {
        if (!$this->dateTimeParameters) {
            return [];
        }
        $datetimes = [];
        for ($i = 0; $i < $this->amountOfParameters; ++$i) {
            $datetime = \DateTime::createFromFormat($format, $parameters[$i]);
            if ($datetime === false) {
                throw new ValidationException('"'.$this->type.'" expects a date of the format "'.$format.'".');
            }
            $datetimes[] = $datetime;
        }
        return $datetimes;
    }