H: selectOneMenu with custom object

I am trying to implement two <h:selectOneMenu/>

The first contains a Type 1 object. When the user selects an object from this list, the second is displayed <h:selectOneMenu/>.

Here is my code

XHTML

<h:form>
<h:selectOneMenu value="#{handler.selectedType1}" valueChangeListener="#{handler.valueChanged}">
    <f:selectItems value="#{handler.types1}" var="type1" itemValue="#{type1.name}" itemLabel="#{type1.name}" />
    <a4j:ajax event="valueChange" render="type2List" execute="@this"/>
</h:selectOneMenu>
<h:selectOneMenu id="type2List" value="#{handler.selectedType2}" rendered="#{not empty handler.selectedType2}">
    <f:selectItems value="#{handler.types2}" var="type2" itemLabel="#{type2.name}" />
</h:selectOneMenu>
</h:form>

bean

@ManagedBean
@ViewScoped
public class Handler {

    private Type1 selectedType1;
    private List<Type1> types1;
    private Type2 selectedType2;
    private List<Type2> types2;

        //getters, setters

        public void valueChanged(ValueChangeEvent event) {
        variants.clear();
        if (event.getNewValue() != null) {
            System.out.println("new value: " + event.getNewValue());
                        // Fill the second list
        }
    }
}

Type1 and Type2 are user classes. Their name attribute is a string.

The problem is that when I select an item from the first list, I get

    24 févr. 2013 12:15:26 com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer getConvertedValue
GRAVE: Could not instantiate converter for type class com.flightfaq.beans.business.AircraftType: java.lang.NullPointerException
24 févr. 2013 12:15:26 com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer getConvertedValue
GRAVE: 
java.lang.NullPointerException
    at com.sun.faces.renderkit.html_basic.HtmlBasicInputRenderer.getConvertedValue(HtmlBasicInputRenderer.java:129)
    at com.sun.faces.renderkit.html_basic.MenuRenderer.convertSelectOneValue(MenuRenderer.java:201)
    at com.sun.faces.renderkit.html_basic.MenuRenderer.getConvertedValue(MenuRenderer.java:318)
    at javax.faces.component.UIInput.getConvertedValue(UIInput.java:1030)
    at javax.faces.component.UIInput.validate(UIInput.java:960)
    at javax.faces.component.UIInput.executeValidate(UIInput.java:1233)
    at javax.faces.component.UIInput.processValidators(UIInput.java:698)
    at org.richfaces.context.PartialViewExecuteVisitCallback.visit(PartialViewExecuteVisitCallback.java:55)
    at org.richfaces.context.BaseExtendedVisitContext.invokeVisitCallback(BaseExtendedVisitContext.java:321)
    at javax.faces.component.UIComponent.visitTree(UIComponent.java:1612)
    at javax.faces.component.UIComponent.visitTree(UIComponent.java:1623)
    at javax.faces.component.UIForm.visitTree(UIForm.java:371)
    at javax.faces.component.UIComponent.visitTree(UIComponent.java:1623)
    at javax.faces.component.UIComponent.visitTree(UIComponent.java:1623)
    at javax.faces.component.UIComponent.visitTree(UIComponent.java:1623)
    at javax.faces.component.UIComponent.visitTree(UIComponent.java:1623)
    at org.richfaces.context.ExtendedPartialViewContextImpl.executeComponents(ExtendedPartialViewContextImpl.java:237)
    at org.richfaces.context.ExtendedPartialViewContextImpl.processPartialExecutePhase(ExtendedPartialViewContextImpl.java:217)
    at org.richfaces.context.ExtendedPartialViewContextImpl.processPartial(ExtendedPartialViewContextImpl.java:196)
    at javax.faces.component.UIViewRoot.processValidators(UIViewRoot.java:1167)
    at com.sun.faces.lifecycle.ProcessValidationsPhase.execute(ProcessValidationsPhase.java:76)
    at com.sun.faces.lifecycle.Phase.doPhase(Phase.java:101)
    at com.sun.faces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:118)
    at javax.faces.webapp.FacesServlet.service(FacesServlet.java:593)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.tomee.catalina.OpenEJBValve.invoke(OpenEJBValve.java:45)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
    at java.lang.Thread.run(Thread.java:680)

I assume that the valueChangeListener property in the first select element is trying to run my managed bean method "valueChanged". But it is stopped until it is reached (I printed something inside and it does not appear in the java console before the exception is thrown)

Is there a problem with Type1 and Type2 not being strings? How can i fix this?

EDIT: after BalusC's answer, this is my code:

XHTML

    <h:form>
        <h:selectOneMenu value="#{missionHandler.selectedAircraftType}" converter="#{missionHandler.acTypeConverter}">
            <f:selectItems value="#{missionHandler.aircraftTypes}" var="type" itemValue="#{type}" itemLabel="#{type.typeOACI}" />
            <f:ajax listener="#{missionHandler.changeSelectedAircraftType}" render="variantsMenu"/>
        </h:selectOneMenu>
        <h:selectOneMenu id="variantsMenu" value="#{missionHandler.selectedVariant}" converter="#{missionHandler.variantConverter}">
            <f:selectItems value="#{missionHandler.variants}" var="variant" itemValue="#{variant}" itemLabel="#{variant.commercialName}" />
        </h:selectOneMenu>
    </h:form>

bean

@ManagedBean
@ViewScoped
public class MissionHandler implements Serializable {

    private static final long serialVersionUID = 2462652101518266609L;

    private Mission mission;

    @EJB
    private AircraftTypeDao aircraftTypeDao;

    @EJB
    private VariantDao variantDao;

    private AircraftType selectedAircraftType;

    private List<AircraftType> aircraftTypes;

    private Variant selectedVariant;

    private List<Variant> variants;

    private AircraftTypeConverter acTypeConverter;

    private VariantConverter variantConverter;

    public MissionHandler() {
        /** Create an empty mission */
        mission = new Mission();
    }

    @PostConstruct
    public void init() {
        aircraftTypes = aircraftTypeDao.findAll();
    }


    public void changeSelectedAircraftType(AjaxBehaviorEvent event) {
        System.out.println("Listener call");
        variants=variantDao.find(selectedAircraftType);
        System.out.println("Listener out");
    }
}

converters

@FacesConverter(forClass=AircraftType.class)
public class AircraftTypeConverter implements Converter, Serializable {

    private static final long serialVersionUID = 7053414108213420057L;

    private final AircraftTypeDao aircraftDao = new AircraftTypeDaoImpl();

    @Override
    public Object getAsObject(FacesContext context, UIComponent component,
            String value) {
        System.out.println("convert to Object " + value);
        AircraftType acType = aircraftDao.find(value);
        System.out.println("got ac type " + acType.getTypeOACI());
        return acType;
    }

    @Override
    public String getAsString(FacesContext context, UIComponent component,
            Object value) {
        System.out.println("convert to String " + value);
        return ((AircraftType) value).getTypeOACI();
    }

}

@FacesConverter(forClass=Variant.class)
public class VariantConverter implements Converter, Serializable {

    private static final long serialVersionUID = 7053414108213420057L;

    private final VariantDao variantDao = new VariantDaoImpl();

    @Override
    public Object getAsObject(FacesContext context, UIComponent component,
            String value) {
        System.out.println("convert to Object " + value);
        Variant variant = variantDao.find(value);
        System.out.println("got variant " + variant.getCommercialName());
        return variant;
    }

    @Override
    public String getAsString(FacesContext context, UIComponent component,
            Object value) {
        System.out.println("convert to String " + value);
        return ((Variant) value).getCommercialName();
    }

}

: - - , AircraftType ( ) . , "" selectOneMenu

:)