Spring Boot with Validation - Inject repository inside custom validator gives Null

Question

Although I found some similar problems (here and here for example) it did not completely answer my problem, as I used spring Boot 2.4.4, or simply don't work. My problem is that repository becomes null during second (JPA) validation. Here is the detail :

I use Spring Boot, and Bean Validation, via the spring-boot-starter-validation dependency. I have a custom validator to check if an email exists in database. First I declare the @EmailExisting annotation :

@Documented
@Constraint(validatedBy = EmailValidator.class)
@Target( { ElementType.METHOD, ElementType.FIELD })
@Retention(RetentionPolicy.RUNTIME)
public @interface EmailExisting {
    String message() default "Email already exists";
    Class<?>[] groups() default {};
    Class<? extends Payload>[] payload() default {};
}

Then the custom validator, with the repository injected to check Database :

public class EmailValidator implements
        ConstraintValidator<EmailExisting, String> {

    @Autowired
    UserRepository userRepository;

    @Override
    public boolean isValid(String email,
                           ConstraintValidatorContext cxt) {
        List<User> users = userRepository.findByEmail(email);
        if (!users.isEmpty()) {
            return false;
        }
        return true;
    }
}

Finally the SPRING MVC part, with the @Valid annotation to trigger validation :

    @Autowired
    UserRepository userRepository;

    @PostMapping(value = "/users")
    public ResponseEntity addUSer(@Valid @RequestBody User user) {

        user.setEmail(user.getEmail());
        user.setLastName(StringUtils.capitalize(user.getLastName()));
        user.setFirstName(StringUtils.capitalize(user.getFirstName()));
        userRepository.save(user);

        return new ResponseEntity(user, HttpStatus.CREATED);
    }

Problem: When I test the endpoint, I have a NullPointerException. At first, during MVC validation the repository is correctly injected. But after, when we call save() method to save the entity in the controller, the control triggers again, and the repository becomes null, hence the NullPointerException.

I found a workaround, to deactivate control on JPA side, with the following configuration : spring.jpa.properties.javax.persistence.validation.mode=none

It works well, but I think it should be possible to have the repository injected in the 2 cases?

All code is in my repository

Thank you in advance!