上传媒体文件加了‘’直接为null，不加返会不和法参数

求问，这是为啥？

$url='https://oapi.dingtalk.com/media/upload?access_token='.$token.'&type=image';
  $file['file'] = '@'.(realpath('/Public/images/128.jpg'));  
  $send=$this->dingtalkcurl($url,$file);

public function dingtalkcurl($url,$data=null){
        $curl = curl_init();
        curl_setopt($curl, CURLOPT_URL, $url);
        curl_setopt($curl, CURLOPT_SSL_VERIFYPEER, FALSE);
        curl_setopt($curl, CURLOPT_SSL_VERIFYHOST, FALSE);
        curl_setopt ( $ch, CURLOPT_SAFE_UPLOAD, false);
        if (!empty($data)){
            curl_setopt($curl, CURLOPT_POST, 1);
            curl_setopt($curl, CURLOPT_POSTFIELDS, $data);
            curl_setopt($curl, CURLOPT_HTTPHEADER,array('Content-Type:multipart/form-data;charset=UTF-8'));
        }
        curl_setopt($curl, CURLOPT_RETURNTRANSFER, 1);
        $output = curl_exec($curl);
        curl_close($curl);
        return json_decode($output,true);
    }