optimize code

src/main/java/com/faf223/expensetrackerfaf/controller/UserController.java

@@ -13,8 +13,12 @@ import org.springframework.web.bind.annotation.RestController;
 @RequestMapping("/users")
 public class UserController {
 
+    private final UserService userService;
+
     @Autowired
-    private UserService userService;
+    public UserController(UserService userService) {
+        this.userService = userService;
+    }
 
     @GetMapping("/{userUuid}")
     public ResponseEntity<User> getUser(@PathVariable String userUuid) {