Trying to get property of non-object

I'm having problems with the code I created, but I've tried it and there's no result.

file controller : portal.php

function pembayaran(){
		$kode = $this->auth['kode'];
		
		$stsConfirm = $this->db2->query("SELECT stsApplyPaid, stsApplyPaidConfirm, applyBankTransferAmount, kode_voucher FROM adis_smb_form WHERE kode = '$kode'")->row();
		$voucher = $stsConfirm->kode_voucher;
		$transfer_amount = $stsConfirm->applyBankTransferAmount;
		
		$cmb = $this->mportal->mCmb($kode);

		$year = date('Y');
		$minYearLulus = $year - 4;
		$dataVoucher = null;

		if ($voucher) {
			$dataVoucher = $this->mportal->getDataVoucher($voucher);
		}		
		
		$harga = $this->mportal->getTotalBayar($dataVoucher->kode_voucher); // error from here
		
		
		$this->smarty->assign([
			'biaya' => $harga,
			'kode_voucher' => $voucher,
			'data_voucher' => $dataVoucher,
			'transfer_amount' => $transfer_amount,
			'breadcum' => $breadcum,
			'site' => $site,
		]);
		// $this->smarty->assign('biaya', $harga);
		// $this->smarty->assign('kode_voucher', $voucher);
		$this->mportal->selectType();
		// $this->smarty->assign("breadcum", $breadcum);
		$this->smarty->display("portal/index.html");
	}

file model : mPortal.php

class Mportal extends CUTI_Model{
	protected $hargaAwal = 350000;

	function __construct(){
		parent::__construct();
	}
	
	function Mportal(){
		parent::__construct();
		
		$this->db2->query("SET lc_time_names = 'id_ID'");
	}
	function getDataVoucher($kodeVoucher){
		$data = $this->db2->query("SELECT * FROM tbl_voucher WHERE kode_voucher = '$kodeVoucher' ")->row();		
		return $data;
	}
	

	function getTotalBayar($kodeVoucher = null){
		$dataVoucher = $this->getDataVoucher($kodeVoucher);

		// if(!$dataVoucher){
		// 	return $this->hargaAwal;
		// }

		// $totalBayar = ($this->hargaAwal - $dataVoucher->discount);

		if($dataVoucher && property_exists($dataVoucher, 'discount')){
        	$totalBayar = ($this->hargaAwal - $dataVoucher->discount);
		} else {
			$totalBayar = $this->hargaAwal;
		}

		return $totalBayar;
	}
}