one endpoint giving me error

[Ampta]

bold part is not working in my system

errors are:
at com.ampta.central_shops.service.cart.CartService.initializeNewCart(CartService.java:53) ~[classes/:na]
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103) ~[na:na]
at java.base/java.lang.reflect.Method.invoke(Method.java:580) ~[na:na]
at org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:355) ~[spring-aop-6.1.13.jar:6.1.13]
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:716) ~[spring-aop-6.1.13.jar:6.1.13]
at com.ampta.central_shops.service.cart.CartService$$SpringCGLIB$$0.initializeNewCart() ~[classes/:na]
at com.ampta.central_shops.controller.CartItemController.addItemToCart(CartItemController.java:32) ~[classes/:na]
at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:103) ~[na:na]
at java.base/java.lang.reflect.Method.invoke(Method.java:580) ~[na:na]

@PostMapping("/item/add")
public ResponseEntity addItemToCart(@RequestParam(required = false) Long cartId,
@RequestParam Long productId,
@RequestParam Integer quantity){
try {

        **if (cartId == null) {
            cartId = cartService.initializeNewCart();
        }**


        cartItemService.addItemToCart(cartId, productId, quantity);
        return ResponseEntity.ok(new ApiResponse("Add Item Success", null));
    }catch (ResourceNotFoundException e){
        return ResponseEntity.status(NOT_FOUND).body(new ApiResponse(e.getMessage(), null));
    }

}

[YunussEmree]

Hey, in this code there is no auto initialize cart for default users so you can set the userid manually or integrate spring security. It will be solution for your problem.