Cara Mengatasi Error di sebuah Aplikasi pada Library PHPExcell

Assalam,.. artinya pada file excel tidak boleh ada yang kosong kolomnya,
ini mau import data ya gan?
 
controller import bikin begini saja :
public function import_excel(){
        $config['upload_path'] = 'asset/'.$this->uri->segment(3);
        $config['allowed_types'] = 'xlsx|xls';
        $this->load->library('upload', $config);
        if ( ! $this->upload->do_upload('fileexcel')){
            $error = array('error' => $this->upload->display_errors());
        }else{
            $data = array('upload_data' => $this->upload->data());
            $upload_data = $this->upload->data(); //Mengambil detail data yang di upload
            $filename = $upload_data['file_name'];//Nama File
            $this->model_app->import_excel($this->uri->segment(3),$filename);
            redirect('controller_nganu');
        }
}
 
Modelsnya begini :
public function import_excel_borongan($directory,$filename){
    ini_set('memory_limit', '-1');
    $inputFileName = './asset/'.$directory.'/'.$filename;
    try {
    $objPHPExcel = PHPExcel_IOFactory::load($inputFileName);
    } catch(Exception $e) {
    die('Error loading file :' . $e->getMessage());
    }
 
    $worksheet = $objPHPExcel->getActiveSheet()->toArray(null,true,true,true);
    $numRows = count($worksheet);
    for ($i=2; $i < ($numRows+1) ; $i++) { 
      $a        = $worksheet[$i]['A'];
      $b        = $worksheet[$i]['B'];
      $c        = $worksheet[$i]['C'];
      $d        = $worksheet[$i]['D'];
 
      $data = array('field1'=>$a,
                    'field1'=>$b,
                    'field1'=>$c,
                    'field1'=>$d);
    $this->model_app->insert('rb_table',$data);
    }
}

Assalam,.. 
itu mau export gan
 

Assalam,.. 
gimna ya gan caranya
 

Assalam,.. coba sesuaikan dengan ini gan file exportnya :
<?php
//load our new PHPExcel library
$this->load->library('excel');
//activate worksheet number 1
$this->excel->setActiveSheetIndex(0);
//name the worksheet
$this->excel->getActiveSheet()->setTitle('Users list');
 
// load database
$this->load->database();
 
// load model
$this->load->model('userModel');
 
// get all users in array formate
$users = $this->userModel->get_users();
 
// read data to active sheet
$this->excel->getActiveSheet()->fromArray($users);
 
$filename='just_some_random_name.xls'; //save our workbook as this file name
header('Content-Type: application/vnd.ms-excel'); //mime type
header('Content-Disposition: attachment;filename="'.$filename.'"'); //tell browser what's the file name
header('Cache-Control: max-age=0'); //no cache
 
//save it to Excel5 format (excel 2003 .XLS file), change this to 'Excel2007' (and adjust the filename extension, also the header mime type)
//if you want to save it as.XLSX Excel 2007 format
$objWriter = PHPExcel_IOFactory::createWriter($this->excel, 'Excel5'); 
 
//force user to download the Excel file without writing it to server's HD
$objWriter->save('php://output');