protected function humandatetimeToIso($humandatetime)
    {
        $datetime = \DateTime::createFromFormat( $this->format, $humandatetime);
        if (!$datetime) return '';
        $timestamp = $datetime->getTimestamp();
        if ($timestamp < 1) {
            return "";
        }
        $humandatetime = date($this->store_as, $timestamp);

        return $humandatetime;
    }