how to make upload file is optional in codeigniter?

Question

I have some problems. I want to upload file as an optional field, but didnt work with my code. How i can solve this?

controllers

public function zoom_request()
{
   $file = ''; // init as blank otherwise notice
    if (!empty($_FILES) && !empty($_FILES['file']['name']))  {
        $config['upload_path'] = './lampiran/request/';
        $config['allowed_types'] = 'pdf|rar|zip|doc|docx|ppt|pptx|jpg|png';
        $config['overwrite'] = TRUE;
        $config['max_size'] = 10000; //3 * 1024 * 1024; //3Mb; 0=unlimited
        $config['max_width']  = 10000; //"3850"; //'1024';
        $config['max_height']  = 10000;
        $this->upload->initialize($config);
        $this->load->library('upload', $config);
        if (!$this->upload->do_upload('file')) {
            redirect('zoom/zoom_request');
        }
        else {
            $media = $this->upload->data();
            $inputFileName = './lampiran/complain/' . $media['file_name'];
            $data = array(
                'id_pegawai' => $this->input->post('id_pegawai'),
                'nama_pic' => $this->input->post('nama_pic'),
            );
            //if the insert data returned true then we show the flash message
            if ($this->Zoom_model->add_request($data)) {
                $data['flash_message'] = TRUE;
            } else {
                $data['flash_message'] = FALSE;
            }
        }
    }
}