not show cart product page when i click button cart

[fain]

hi.

in product page, i have 3 grid table of product by top sale, new product & preloved product.

but when i cart 1 from top sale, new product & preloved product, every cart inserted into DB. but when i click Cart to show product cart. It shows error like below. show cart page can only display when i cart nothing. Errors show at page & my controller are below:

ErrorException in CartController.php line 53:
Trying to get property of non-object
in CartController.php line 53

Error for localhost/cart:
at HandleExceptions->handleError('8', 'Trying to get property of non-object', 'C:\www\eshop_laravel\app\Http\Controllers\CartController.php', '53', array('cart' => object(Cart), 'items' => object(Collection), 'total' => '0', 'item' => object(CartItem))) in CartController.php line 53
at CartController->showCart()
at call_user_func_array(array(object(CartController), 'showCart'), array()) in Controller.php line 55
at Controller->callAction('showCart', array()) in ControllerDispatcher.php line 44
at ControllerDispatcher->dispatch(object(Route), object(CartController), 'showCart') in Route.php line 189
at Route->runController() in Route.php line 144
at Route->run(object(Request)) in Router.php line 653
at Router->Illuminate\Routing{closure}(object(Request)) in Pipeline.php line 53
at Pipeline->Illuminate\Routing{closure}(object(Request)) in SubstituteBindings.php line 41
at SubstituteBindings->handle(object(Request), object(Closure)) in Pipeline.php line 137
at Pipeline->Illuminate\Pipeline{closure}(object(Request)) in Pipeline.php line 33
at Pipeline->Illuminate\Routing{closure}(object(Request)) in Authenticate.php line 43
at Authenticate->handle(object(Request), object(Closure)) in Pipeline.php line 137
at Pipeline->Illuminate\Pipeline{closure}(object(Request)) in Pipeline.php line 33
at Pipeline->Illuminate\Routing{closure}(object(Request)) in VerifyCsrfToken.php line 65
at VerifyCsrfToken->handle(object(Request), object(Closure)) in Pipeline.php line 137
at Pipeline->Illuminate\Pipeline{closure}(object(Request)) in Pipeline.php line 33
at Pipeline->Illuminate\Routing{closure}(object(Request)) in ShareErrorsFromSession.php line 49
at ShareErrorsFromSession->handle(object(Request), object(Closure)) in Pipeline.php line 137
at Pipeline->Illuminate\Pipeline{closure}(object(Request)) in Pipeline.php line 33
at Pipeline->Illuminate\Routing{closure}(object(Request)) in StartSession.php line 64
at StartSession->handle(object(Request), object(Closure)) in Pipeline.php line 137
at Pipeline->Illuminate\Pipeline{closure}(object(Request)) in Pipeline.php line 33
at Pipeline->Illuminate\Routing{closure}(object(Request)) in AddQueuedCookiesToResponse.php line 37
at AddQueuedCookiesToResponse->handle(object(Request), object(Closure)) in Pipeline.php line 137
at Pipeline->Illuminate\Pipeline{closure}(object(Request)) in Pipeline.php line 33
at Pipeline->Illuminate\Routing{closure}(object(Request)) in EncryptCookies.php line 59
at EncryptCookies->handle(object(Request), object(Closure)) in Pipeline.php line 137
at Pipeline->Illuminate\Pipeline{closure}(object(Request)) in Pipeline.php line 33
at Pipeline->Illuminate\Routing{closure}(object(Request)) in Pipeline.php line 104
at Pipeline->then(object(Closure)) in Router.php line 655
at Router->runRouteWithinStack(object(Route), object(Request)) in Router.php line 629
at Router->dispatchToRoute(object(Request)) in Router.php line 607
at Router->dispatch(object(Request)) in Kernel.php line 268
at Kernel->Illuminate\Foundation\Http{closure}(object(Request)) in Pipeline.php line 53
at Pipeline->Illuminate\Routing{closure}(object(Request)) in CheckForMaintenanceMode.php line 46
at CheckForMaintenanceMode->handle(object(Request), object(Closure)) in Pipeline.php line 137
at Pipeline->Illuminate\Pipeline{closure}(object(Request)) in Pipeline.php line 33
at Pipeline->Illuminate\Routing{closure}(object(Request)) in Pipeline.php line 104
at Pipeline->then(object(Closure)) in Kernel.php line 150
at Kernel->sendRequestThroughRouter(object(Request)) in Kernel.php line 117
at Kernel->handle(object(Request)) in index.php line 53
at require_once('C:\www\eshop_laravel\public\index.php') in server.php line 21

My CartController:

middleware('auth'); } public function addItem ($productId){ $cart = Cart::where('user_id',Auth::user()->id)->first(); if(!$cart){ $cart = new Cart(); $cart->user_id=Auth::user()->id; $cart->save(); } $cartItem = new Cartitem(); $cartItem->product_id=$productId; $cartItem->cart_id= $cart->id; $cartItem->save(); return redirect('/cart'); } public function showCart(){ $cart = Cart::where('user_id',Auth::user()->id)->first(); if(!$cart){ $cart = new Cart(); $cart->user_id=Auth::user()->id; $cart->save(); } $items = $cart->cartItems; $total=0; foreach($items as $item){ line 53 ---> $total+=$item->product->price; } return view('front.cart',['items'=>$items,'total'=>$total]); } public function removeItem($id){ CartItem::destroy($id); return redirect('/cart'); } } pls help me. very big thanks for any helpers .