public function getNextVersion($from)
    {
        $found = false;
        foreach (array_keys($this->versions) as $timestamp) {
            if ($from === null) {
                return $timestamp;
            }

            if ($timestamp == $from) {
                $found = true;
                continue;
            }

            if ($found) {
                return $timestamp;
            }
        }

        return;
    }