java.lang.ClassCastException: java.lang.String cannot be cast to [Ljava.lang.Object; when trying to get colum values to a list by Hibernate

I'm developing a spring web application with Hibernate. I have faced an error when getting column values from a table to a list. But this error keeps coming. Please help me put. Thanks in advance.

@Repository
@Transactional
public class GetProjectsDaoImpl implements GetProjectsDao {

    @Autowired
    private HibernateUtilImpl  hibernateutilimpl;

    public List<Projects> getProjects() {

        String sql = "select project_id from project";

        List<Object[]> projectObjects = hibernateutilimpl.fetchAll(sql);

        List<Projects> projectsList = new ArrayList<Projects>();

        for(Object[] projectObject: projectObjects) {
            Projects project = new Projects();
            String id = (String) projectObject[0];

            project.setProjectId(id);

            projectsList.add(project);
        }
        return projectsList;
    }

}

@Repository
public class HibernateUtilImpl implements HibernateUtil {

    @Autowired
    private SessionFactory sessionFactory;

    public <T> Serializable create(final T entity) {

        return sessionFactory.getCurrentSession().save(entity);
    }

    public <T> T update(final T entity) {
        sessionFactory.getCurrentSession().update(entity);
        return entity;
    }

    public <T> void delete(final T entity) {

        sessionFactory.getCurrentSession().delete(entity);
    }

    @SuppressWarnings("rawtypes")
    public <T> List<T> fetchAll(String query) {
        return sessionFactory.getCurrentSession().createNativeQuery(query).list();
    }

}