Hibernate CriteriaクエリでWHERE～IS NULL/IS NOT NULL

<hibernate-mapping>
    <class name="eg.Son" table="SON">
        <id name="id" unsaved-value="0">
             <generator class="increment"/>
        </id>
        <property name="name" column="NAME" type="string" length="100"/>
        
        <many-to-one
            column="FATHER_ID"
            name="father"
            class="eg.Father"
            not-null="true"
            cascade="none" outer-join="true" />
    </class>
</hibernate-mapping>

    public static void testCriteria(Session sess) {
        Criteria criteria = sess.createCriteria(Son.class);
        criteria.add(Restrictions.isNull("name"));    // NAME IS NULL
        
        List list = criteria.list();
        
        System.out.println(list.size());
    }

    public static void testCriteria(Session sess) {
        Criteria criteria = sess.createCriteria(Son.class);
        criteria.add(Restrictions.isNull("father"));        //son.FATHER_ID IS NULL
        
        List list = criteria.list();
        
        System.out.println(list.size());
    }