'u' Replaced By 'U' Is A Big Error,Insight From My On Going Spring Boot Project

A developer building an AI-aided e-commerce project with Spring Boot, OpenAI models, and BLIP-CLIP models spent three days debugging a cart endpoint that returned 'The given id must not be null'. The issue was caused by DTO field names starting with capital letters (e.g., 'UserId' instead of 'userId'), which broke JSON deserialization. The developer emphasizes the importance of following naming conventions to avoid such errors.

For Three days I was struck on running my Cart endpoints.Everything seems correct. But the Error on running the endpoint was : { "success": false, "message": "The given id must not be null", "data": null } Somewhere the ID was becoming null before it reaches the repository even when i was passing the Id. Let me first clear the endpoints and scenario to you. I am Building an Full Fledged AI-aided E-com project using spring boot,OpenAI Models and BLIP-CLIP models for the Image-to-Text and Text-to-Image processing. Right now,I am creating the Entities,Repository,Services and Controllers for basic working of the website. I am also using DTO's for the structured data transfer. The problem started with Cart endpoints,my 'addToCart' service was not actually adding the products into the cart even when I was passing the values I was getting the id to be null. /cart/addToCart Request body application/json Example Value Schema { "userId": 9007199254740991, "productId": 9007199254740991, "quantity": 1073741824 } Response { "success": boolean, "message": "string", "data": "string" } I queried all the sources and I was getting more confused,Nothing Clearly was error there in my code yet the endpoints were not responsing. checklist : @RequestBody for JSON data sent in a POST or PUT body. @RequestParam for query parameters in the URL like ?name=test . @PathVariable for variables built directly into the URL path like /users/{id} .Ensure your JSON property names match your Java class variable names exactly. Verify that your DTO class has getter and setter methods or use Lombok @Data or @Getter / @Setter , which Jackson needs to read the data. Check that the Content-Type header in your client request is set to application/json when sending a JSON body. Lets take one example,we are creating a cart service in an e-com project and we have this controller for add to cart service. ResponseEntity<ApiResponse<String addToCart @RequestBody CartRequest request { String status = service.addToCart request ; ApiResponse<String response = new ApiResponse< true, "Added", status ; return ResponseEntity.ok response ; } With the response DTO as cartRequest as follows: public class CartRequest { @NotNull @Positive private Long UserId; @NotNull @Positive private Long ProductId; @NotNull @Positive @Min 1 private Integer Quantity; } Everything is in sync right? Congrats you have hit the error. Remember? Ensure your JSON property names match your Java class variable names exactly. This is the error I was struck into, this the 'u' replaced with 'U'.Notice the Capital letter at the beginning of the the DTO variables. public class CartRequest { @NotNull @Positive private Long ~~UserId;~~ @NotNull @Positive private Long ~~ProductId;~~ @NotNull @Positive @Min 1 private Integer ~~Quantity;~~ } Conventions Matters and not every advice and error handling will be provided to you as such. keep Things in mind and follow conventions for devlopment.