Attempt to read property "type" on null (product_data)

public function calculateAverageCOGS($product_sale_data) { $product_cost = 0; foreach ($product_sale_data as $key => $product_sale) { $product_data = Product::select('type', 'product_list', 'variant_list', 'qty_list')->find($product_sale->product_id); if($product_data->type == 'combo') { $product_list = explode(",", $product_data->product_list); if($product_data->variant_list) $variant_list = explode(",", $product_data->variant_list); else $variant_list = []; $qty_list = explode(",", $product_data->qty_list);

            foreach ($product_list as $index => $product_id) {
                if(count($variant_list) && $variant_list[$index]) {
                    $product_purchase_data = ProductPurchase::where([
                        ['product_id', $product_id],
                        ['variant_id', $variant_list[$index] ]
                    ])
                    ->select('recieved', 'purchase_unit_id', 'total')
                    ->get();
                }
                else {
                    $product_purchase_data = ProductPurchase::where('product_id', $product_id)
                    ->select('recieved', 'purchase_unit_id', 'total')
                    ->get();
                }
                $total_received_qty = 0;
                $total_purchased_amount = 0;
                $sold_qty = $product_sale->sold_qty * $qty_list[$index];
                foreach ($product_purchase_data as $key => $product_purchase) {
                    $purchase_unit_data = Unit::select('operator', 'operation_value')->find($product_purchase->purchase_unit_id);
                    if($purchase_unit_data->operator == '*')
                        $total_received_qty += $product_purchase->recieved * $purchase_unit_data->operation_value;
                    else
                        $total_received_qty += $product_purchase->recieved / $purchase_unit_data->operation_value;
                    $total_purchased_amount += $product_purchase->total;
                }
                if($total_received_qty)
                    $averageCost = $total_purchased_amount / $total_received_qty;
                else
                    $averageCost = 0;
                $product_cost += $sold_qty * $averageCost;
            }
        }
        else {
            if($product_sale->product_batch_id) {
                $product_purchase_data = ProductPurchase::where([
                    ['product_id', $product_sale->product_id],
                    ['product_batch_id', $product_sale->product_batch_id]
                ])
                ->select('recieved', 'purchase_unit_id', 'total')
                ->get();
            }
            elseif($product_sale->variant_id) {
                $product_purchase_data = ProductPurchase::where([
                    ['product_id', $product_sale->product_id],
                    ['variant_id', $product_sale->variant_id]
                ])
                ->select('recieved', 'purchase_unit_id', 'total')
                ->get();
            }
            else {
                $product_purchase_data = ProductPurchase::where('product_id', $product_sale->product_id)
                ->select('recieved', 'purchase_unit_id', 'total')
                ->get();
            }
            $total_received_qty = 0;
            $total_purchased_amount = 0;
            if($product_sale->sale_unit_id) {
                $sale_unit_data = Unit::select('operator', 'operation_value')->find($product_sale->sale_unit_id);
                if($sale_unit_data->operator == '*')
                    $sold_qty = $product_sale->sold_qty * $sale_unit_data->operation_value;
                else
                    $sold_qty = $product_sale->sold_qty / $sale_unit_data->operation_value;
            }
            else {
                $sold_qty = $product_sale->sold_qty;
            }
            foreach ($product_purchase_data as $key => $product_purchase) {
                $purchase_unit_data = Unit::select('operator', 'operation_value')->find($product_purchase->purchase_unit_id);
                if($purchase_unit_data->operator == '*')
                    $total_received_qty += $product_purchase->recieved * $purchase_unit_data->operation_value;
                else
                    $total_received_qty += $product_purchase->recieved / $purchase_unit_data->operation_value;
                $total_purchased_amount += $product_purchase->total;
            }
            if($total_received_qty)
                $averageCost = $total_purchased_amount / $total_received_qty;
            else
                $averageCost = 0;
            $product_cost += $sold_qty * $averageCost;
        }
    }
    return $product_cost;
}