hibernate session.createQuery() keeps getting an ArrayIndexOutOfBoundsException

Question

I'm new to hibernate and currently struggling with setting up a Rest-API.

When I try to fetch all objects, it works fine and I also can search for an object by its ID. But when I try to use an HQL query (even a simple one like 'from CustomObject'), it won't work.

I somehow managed to get (seamingly) sessionFactory to work, so I can get a Session object for creation of HQL-Queries. But at the moment, when session.createQuery() is called, I always get an ArrayIndexOutOfBoundsException.

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Here's my function, where the problem is happening:

public List<CustomObject> findByHQL() {
        Configuration conf = new Configuration().configure();
        SessionFactory sessionFactory = conf.buildSessionFactory();
        Session session = sessionFactory.openSession();


        String hqlQueryString = "from com.blackfake.hibernate_query_test.orm.CustomObject o";

        Query<CustomObject> hqlQuery = session.createQuery(hqlQueryString, CustomObject.class);
//        NativeQuery<CustomObject> sqlQuery = session.createSQLQuery("select id, name, price from objects");
        return hqlQuery.list();
    }

Session and SessionFactory are from org.hibernate package

Configuration is from org.hibernate.cfg

what I find even more confusing, is, that the createSQLQuery() method does work without any problem …

Maybe I should mention, that my DB is a PostgreSQL ;)

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The Error:

java.lang.ArrayIndexOutOfBoundsException: Index 0 out of bounds for length 0
    at org.hibernate.internal.AbstractSharedSessionContract.resultClassChecking(AbstractSharedSessionContract.java:862) ~[hibernate-core-5.6.7.Final.jar:5.6.7.Final]
    at org.hibernate.internal.AbstractSharedSessionContract.createQuery(AbstractSharedSessionContract.java:849) ~[hibernate-core-5.6.7.Final.jar:5.6.7.Final]
    at org.hibernate.internal.AbstractSharedSessionContract.createQuery(AbstractSharedSessionContract.java:114) ~[hibernate-core-5.6.7.Final.jar:5.6.7.Final]