java sample web service started with "java.lang.NullPointerException", how to fix?

I've got a simple java web service sample program from the internet:

import javax.jws.WebParam; import javax.jws.WebService; import javax.xml.ws.Endpoint; import java.util.Date;

@WebService
interface IService {
    void hello(@WebParam(name="username") String username);
}

@WebService(targetNamespace = "ServiceImpl", endpointInterface="IService")
class ServiceImp implements IService{
    @Override
    public void hello(@WebParam(name = "username") String username) {
        System.out.println("hello " + username + " now is " + new Date());
    }
}

public class ServiceMain {
    public static void main(String[] args) {
        String address = "http://localhost:7777/myService";
        Endpoint.publish(address, new ServiceImp());
        System.out.println("OK");
    }
}

It compiles and runs with exception:

Exception in thread "main" java.lang.NullPointerException
at com.sun.xml.internal.ws.model.RuntimeModeler.getPortTypeName(RuntimeModeler.java:1618)
at com.sun.xml.internal.ws.model.RuntimeModeler.getPortTypeName(RuntimeModeler.java:1584)
at com.sun.xml.internal.ws.server.EndpointFactory.create(EndpointFactory.java:226)
at com.sun.xml.internal.ws.server.EndpointFactory.createEndpoint(EndpointFactory.java:144)
at com.sun.xml.internal.ws.api.server.WSEndpoint.create(WSEndpoint.java:563)
at com.sun.xml.internal.ws.api.server.WSEndpoint.create(WSEndpoint.java:545)
at com.sun.xml.internal.ws.transport.http.server.EndpointImpl.createEndpoint(EndpointImpl.java:308)
at com.sun.xml.internal.ws.transport.http.server.EndpointImpl.publish(EndpointImpl.java:231)
at com.sun.xml.internal.ws.spi.ProviderImpl.createAndPublishEndpoint(ProviderImpl.java:126)
at javax.xml.ws.Endpoint.publish(Endpoint.java:240)
at ServiceMain.main(ServiceMain.java:22)

So where does this code snippet get wrong, and how to fix it? Thanks a lot.