public function getSalesInvoiceLines()
    {
        if (array_key_exists('__deferred', $this->attributes['SalesInvoiceLines'])) {
            $this->attributes['SalesInvoiceLines'] = (new SalesInvoiceLine($this->connection()))->filter("InvoiceID eq guid'{$this->InvoiceID}'");
        }

        return $this->attributes['SalesInvoiceLines'];
    }