示例的Spring JPA查询匹配一个空字段，但忽略其他字段

import org.springframework.data.jpa.domain.Specification;
import org.springframework.data.jpa.domain.Specifications;

public class UserRepository {

    public List<User> findUsersWithEmptyField(String fieldName) {
        Specification<User> spec = Specifications.where((root, query, cb) ->
                cb.isNull(root.get(fieldName)));

        return userRepository.findAll(spec);
    }
}