rawPassword cannot be null exception

I have the following problem:

I want to test if a user registers successfully. I'm not doing this over a UI but via Postman. The problem is that I get an exception when I use the POST Command. I have already checked all annotations.

Postman Screenshot

Exception:

java.lang.IllegalArgumentException: rawPassword cannot be null at org.springframework.security.crypto.bcrypt.BCryptPasswordEncoder.encode(BCryptPasswordEncoder.java:103) ~[spring-security-core-5.3.3.RELEASE.jar:5.3.3.RELEASE] at com.example.application.backend.data.service.UserService.singUpUser(UserService.java:41) ~[classes/:na] at com.example.application.backend.data.registration.RegistrationService.register(RegistrationService.java:22) ~[classes/:na] at com.example.application.backend.data.registration.RegistrationController.register(RegistrationController.java:18)

This is my UserService Class:

private final static  String USER_NOT_FOUND_MSG = "user with email %s not found";
@Autowired
private final UserRepository userRepository;
@Autowired
private final BCryptPasswordEncoder bCryptPasswordEncoder;

public UserService(
        UserRepository userRepository,
        BCryptPasswordEncoder bCryptPasswordEncoder) {
    this.userRepository = userRepository;
    this.bCryptPasswordEncoder = bCryptPasswordEncoder;
}

@Override
public UserDetails loadUserByUsername(String email) throws UsernameNotFoundException {
    return userRepository.findByEmail(email)
            .orElseThrow(() ->
                    new UsernameNotFoundException(String.format(USER_NOT_FOUND_MSG, email)));
}

public String singUpUser(User user) {
    boolean userExists = userRepository.findByEmail(user.getEmail()).isPresent();

    if(userExists){
        throw new IllegalStateException("email already taken");
    }

    String encodedPassword = bCryptPasswordEncoder.encode(user.getPassword());

    user.setPassword(encodedPassword);

    userRepository.save(user);

    return "it works";
}

Registration Service Class:

@Autowired
private final UserService userService;
private final EmailValidator emailValidator;

public String register(RegistrationRequest request) {
    boolean isValidEmail = emailValidator.test(request.getEmail());
    if (!isValidEmail) {
        throw new IllegalStateException("email not valid");
    }
    return userService.singUpUser(
            new User(
                    request.getFirstName(),
                    request.getLastName(),
                    request.getEmail(),
                    request.getPassword(),
                    UserRole.USER
            )
    );
}

public RegistrationService(UserService userService, EmailValidator emailValidator) {
    this.userService = userService;
    this.emailValidator = emailValidator;
}

Registration Controller Class:

@Autowired
private RegistrationService registrationService;

@PostMapping
public String register(@RequestBody RegistrationRequest request) {
    return registrationService.register(request);
}