[Spring] - PasswordEncoder 에러

public class MemberController {
    @PostMapping("...")
    public String doModifyPassword(ModifyPasswordDto dto, 
                                   @AuthenticationPrincipal MemberContext context){
        if(checkMatchPassword(context.getMember().getUsername(), dto.getOldPassword())){
            ...
        }
    }
}

public class MemberService{
    @Transactional(readOnly = true)
    public boolean checkMatchPassword(String username, String oldPassword) {
        return passwordEncoder.matches(oldPassword, member.getPassword());
    }
}

public class MemberService {
    // 레거시 코드
    @Transactional(readOnly = true)
    public boolean checkMatchPassword(Member member, String oldPassword) {
        return passwordEncoder.matches(oldPassword, member.getPassword());
    }

    // 개선 코드
    @Transactional(readOnly = true)
    public boolean checkMatchPassword(String username, String oldPassword) {
        Member currentMember = memberRepository.findByUsername(username).orElse(null);
        if (currentMember != null) {
            return passwordEncoder.matches(oldPassword, currentMember.getPassword());
        }
        return false;
    }
}