Apache CXF - credentials not being sent from WSS4JOutInterceptor?

I am trying to connect to a web service using WS-Security UsernameToken spec 1.0, using apache cxf 2.4.0.

I've copied the code below from the CXF docs, but am getting: org.apache.cxf.ws.policy.PolicyException: No username available

    MyService_Service ss = new MyService_Service(wsdlURL, SERVICE_NAME);
    MyService port = ss.getBasicHttpBindingMyService ();  


    Client client = ClientProxy.getClient(port);
    Endpoint cxfEndpoint = client.getEndpoint();

    Map<String,Object> outProps = new HashMap<String,Object>();
    outProps.put(WSHandlerConstants.ACTION, WSHandlerConstants.USERNAME_TOKEN);
    outProps.put(WSHandlerConstants.USER, "USERNAME");
    outProps.put(WSHandlerConstants.PASSWORD_TYPE, WSConstants.PW_TEXT);
    outProps.put(WSHandlerConstants.PW_CALLBACK_CLASS, 
    ClientPasswordHandler.class.getName());

    WSS4JOutInterceptor wssOut = new WSS4JOutInterceptor(outProps);
    cxfEndpoint.getOutInterceptors().add(wssOut);

I've also implemented a ClientPasswordHandler class, again from the docs, but it seems like the username is never sent (according to the error). Here is the password handler:

public class ClientPasswordHandler implements CallbackHandler {
public void handle(Callback[] callbacks) throws IOException, UnsupportedCallbackException {
    WSPasswordCallback pc = (WSPasswordCallback) callbacks[0];
    pc.setPassword("Password");     
    }
}

Is there any way to see if the WSS4Jinterceptor is being applied, and the UsernameToken is sent?