Wicket: Setting value of DropDownChoice with CompoundPropertyModel

I'm filling a form with data from a CompoundPropertyModel. My TextArea and DateTextField get their value by using the name of the field of the Model as the Id so it will look for a Model in it's parents and find the value through reflection, as described in http://ift.tt/2z0uAEg. But I fail to get this working for my DropDownChoice. The value stays null.

Would love to hear if someone knows what I'm doing wrong. Currently have a workarround in place where I give a PropertyModel of the FotoGroep to my DropDownChoice constructor.

Class:

public class ImageControlForm<T extends Foto> extends StatelessForm<Foto> {

    private TextArea<String> beschrijving;
    private DateTextField datum;
    private DropDownChoice<FotoGroep> groep;

    public ImageControlForm(String id, CompoundPropertyModel<Foto> fotoModel) {
        super(id, fotoModel);

        setMultiPart(true);
        setDefaultModel(fotoModel);

        add(maakBeschrijvingField());
        add(maakDatumField());
        add(maakGroepField());
    }

    private TextArea<?> maakBeschrijvingField() {
        beschrijving = new TextArea<>("beschrijving");
        return beschrijving;
    }

    private DateTextField maakDatumField() {
        datum = new DateTextField("datum", "d/M/yy");
        datum.add(new DatumPicker());
        return datum;
    }

    private DropDownChoice<FotoGroep> maakGroepField() {
        Order sortOrder = Helper.createOrder("naam", SortOrder.ASC);
        List<FotoGroep> fotoGroepen = databaseService.getPictureGroups(sortOrder);
        groep = new DropDownChoice<>("fotoGroep", fotoGroepen, new ChoiceRenderer<FotoGroep>("naam", "fotoGroepId"));
        groep.isRequired();
        return groep;
    }

Foto:

@Entity
@Table(name = "XS_FOTO")
public class Foto extends BasisModel implements Serializable {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "FOTO_ID")
    private Long fotoId;

    @Column(name = "BESCHRIJVING", nullable = true)
    private String beschrijving;

    @Column(name = "DATUM", nullable = true)
    @Temporal(TemporalType.DATE)
    private Date datum;

    @ManyToOne
    @JoinColumn(name = "FOTO_GROEP_ID", nullable = false)
    private FotoGroep fotoGroep = new FotoGroep(Long.valueOf(12));

    (getters and setters)

FotoGroep:

@Entity
@Table(name = "XS_FOTO_GROEP")
public class FotoGroep extends BasisModel implements Serializable {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "FOTO_GROEP_ID")
    private Long fotoGroepId;

    @Column(name = "NAAM", nullable = false)
    private String naam;

    (getters and setters)