App\Http\Controllers\InvoiceApiController::prepareItem PHP Method

    private function prepareItem($item)
    {
        // if only the product key is set we'll load the cost and notes
        if (!empty($item['product_key']) && empty($item['cost']) && empty($item['notes'])) {
            $product = Product::findProductByKey($item['product_key']);
            if ($product) {
                if (empty($item['cost'])) {
                    $item['cost'] = $product->cost;
                }
                if (empty($item['notes'])) {
                    $item['notes'] = $product->notes;
                }
            }
        }
        $fields = ['cost' => 0, 'product_key' => '', 'notes' => '', 'qty' => 1];
        foreach ($fields as $key => $val) {
            if (!isset($item[$key])) {
                $item[$key] = $val;
            }
        }
        return $item;
    }