I would like to add, edit and get users via an API I have created. I can add users and get all users added via API requests on Postman but I can't get data for a specific user when I request it on Postman as all I get is a null response with a 200 OK status. How can I be able to get a specific user's information using its national Id?

This is how my entity looks like;

```
public class users {

    @Id
    private String Id;

    @Field("nationalId")
    @JsonProperty("nationalId")
    private String nationalId;

    @Field("userName")
    @JsonProperty("userName")
    private String userName;

    @Field("userEmail")
    @JsonProperty("userEmail")
    private String userEmail;

    @Field("userPin")
    @JsonProperty("userPin")
    private String userPin;

    @Field("userContact")
    @JsonProperty("userContact")
    private String userContact;

    @Field("imageUrl")
    @JsonProperty("imageUrl")
    private String imageUrl;

    @Field("loanLimit")
    @JsonProperty("loanLimit")
    private String loanLimit;

}

```

My controller class looks like this;

```
class Controller {
        @Autowired
        private user_service User_Service;

        @PostMapping("/save_user")
        private users save (@RequestBody users Users){return User_Service.save(Users);}

        @PutMapping("/update_user")
        private users update (@RequestBody users Users){return User_Service.update(Users);}

        @GetMapping("/all")
        private List<users> getAllusers(){return User_Service.getAllusers();}

        @GetMapping("/user/{nationalId}")
        private Optional <users> getusers(@PathVariable String nationalId) {return User_Service.getusers(nationalId);}

        @DeleteMapping("/delete_user/{nationalId}")
        private void deleteUser (@PathVariable String nationalId){User_Service.deleteUser(nationalId);}

    }

```

My user service look like this;

```
public interface user_service {

users save (users Users);

users update (users Users);

List<users> getAllusers();

Optional<users> getusers(String nationalId);

void deleteUser (String nationalId);

}

```