NullPointerException at org.slim3.datastore.ModelQuery.asQueryResultList(ModelQuery.java:295)

PersonTest.java

package pomu0325.model;

import static org.hamcrest.CoreMatchers.is;
import static org.junit.Assert.assertThat;

import org.junit.Test;
import org.slim3.datastore.Datastore;
import org.slim3.datastore.S3QueryResultList;
import org.slim3.tester.AppEngineTestCase;

import pomu0325.meta.PersonMeta;

public class PersonTest extends AppEngineTestCase {
    @Test
    public void test() throws Exception {
        Person pomu0325 = new Person();
        pomu0325.getSkill().add("Java");
        pomu0325.getSkill().add("Scala");
        Datastore.put(pomu0325);
        
        PersonMeta meta = PersonMeta.get();
        S3QueryResultList<Person> result1
            = Datastore.query(meta).filter(meta.skill.in("Java")).asQueryResultList();
        assertThat(result1.size(), is(1));
        
        // NullPointerException is thrown at asQueryResultList() when using InCriterion with 2 or more values... 
        //  at org.slim3.datastore.ModelQuery.asQueryResultList(ModelQuery.java:295)
        S3QueryResultList<Person> result2
            = Datastore.query(meta).filter(meta.skill.in("Java", "Scala")).asQueryResultList();
        assertThat(result2.size(), is(1));
    }
}