public function getApprovalData($startTime, $endTime, $nextSpNum = null)
    {
        $params = [
            'starttime'  => $startTime,
            'endtime'    => $endTime,
            'next_spnum' => $nextSpNum,
        ];

        return $this->parseJSON('json', [self::API_APPROVAL_DATA, $params]);
    }