findMembers() NullPointerException

AOP까지 학습 마친 상태인데 갑자기 member 목록을 보려고 하면 NullPointerException이 뜹니다. 

MemberController에 있는 this.memberService가 null이라고 하는데 왜 그런지 잘 모르겠습니다. 

java.lang.NullPointerException: Cannot invoke "hello.hellospring.service.MemberService.findMembers()" because "this.memberService" is null

at hello.hellospring.controller.MemberController.list(MemberController.java:40) ~[classes/:na]

@Controller
public class MemberController {

    private final MemberService memberService;

    @Autowired   //Dependency Injection
    public MemberController(MemberService memberService) {
        this.memberService = memberService;
    }

    @GetMapping("/members/new")
    public String createForm() {
        return "members/createMemberForm";
    }

    @PostMapping("/members/new")
    public String create(MemberForm form) {
        Member member = new Member();
        member.setName(form.getName());

        memberService.join(member);

        return "redirect:/";
    }

    @GetMapping("/members")
    private String list(Model model) {
        List<Member> members = memberService.findMembers();
        model.addAttribute("members", members);
        return "members/memberList";
    }
}

Description:

The bean 'memberService', defined in class path resource [hello/hellospring/SpringConfig.class], could not be registered. A bean with that name has already been defined in file [C:\Users\강수아\Downloads\hello-spring\hello-spring\out\production\classes\hello\hellospring\service\MemberService.class] and overriding is disabled.

Action:

Consider renaming one of the beans or enabling overriding by setting spring.main.allow-bean-definition-overriding=true