Laravel 5，自参考hasone无法在刀片中工作

Question

全部 我有发票模型，并且有自我参考

\\Invoice Model
public function parentInvoice()
{
    return $this->hasOne('App\Invoice', 'id', 'parent_invoice_id');
}

在web.php中进行测试可以正常工作

Route::get('self', function () {
$parent = Invoice::find(132);
$children = $parent->parentInvoice->invoice_date;
echo $children;
// 2018-06-08 - it's work
});

但是在刀片上不起作用:(为什么？

not work! - <b>Date:</b>&nbsp; {{$invoice->parentInvoice->invoice_date)}} <br /><br />

it's work - <div class="header">Korekta faktury nr {{ $invoice->invoice_date 
   }}</div> 

Error: Trying to get property of non-object

请帮助：（

这是我在发票模型上的功能：

private function generateCreditnoteInvoiceChangeData()
    {
        $config = InvoiceConfig::find(1);
        $pdf = \PDF::loadView(
            'pdf.creditnote_invoice_change_data',
            array(
                'config' => $config,
                'invoice' => $this
            )
        );

        return $pdf;
    }