[SOLVED] SerializationException while deserializing com.google.appengine.api.datastore.Key GWT

I have a RPC-Call :

@Override
public void onSuccess(Void result) {
        Window.alert("SuccessElse");
          userService.getUser("103419018118650635943", new AsyncCallback<User>() {

                @Override
                public void onFailure(Throwable e) {
                    Window.alert("FailAgain");
                    
                    e.printStackTrace();
                }

                @Override
                public void onSuccess(User result) {
                    Window.alert(user.getEmail());
                    
                }
            });

    }

User is :

@Entity
public class User implements IsSerializable {

@Id
@Column(name="id")
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Key id;

private String googleID;

private String firstName;

private String lastName;

private String password;

private String gender;

private String email;


@OneToOne(cascade={CascadeType.ALL})
@JoinColumn(name="key")

private AuthenticationToken token=new AuthenticationToken();

private String pictureStringURL;

private String googlePlusProfileURL;

private String defaultLanguage;

// Lots of Sets and Gets }

Method Called getUser(String googleID):

public User getUser(String googleId){
    EntityManager em = emfInstance.createEntityManager();
    Query q = em
            .createQuery("select  u from User u where u.googleID=:googleId");
    q.setParameter("googleId", googleId);
    
    return (User) q.getResultList().get(0);
}

then I find my Self facing this Exception in How Key can't be deserialized in Client Side

com.google.gwt.user.client.rpc.IncompatibleRemoteServiceException: The response could not be deserialized
    at com.google.gwt.user.client.rpc.impl.RequestCallbackAdapter.onResponseReceived(RequestCallbackAdapter.java:221)
    at com.google.gwt.http.client.Request.fireOnResponseReceived(Request.java:258)
    at com.google.gwt.http.client.RequestBuilder$1.onReadyStateChange(RequestBuilder.java:412)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessagesWhileWaitingForReturn(BrowserChannelServer.java:338)
    at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:219)
    at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:571)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:279)
    at com.google.gwt.dev.shell.JavaScriptHost.invokeNativeObject(JavaScriptHost.java:91)
    at com.google.gwt.core.client.impl.Impl.apply(Impl.java)
    at com.google.gwt.core.client.impl.Impl.entry0(Impl.java:242)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    at java.lang.reflect.Method.invoke(Method.java:597)
    at com.google.gwt.dev.shell.MethodAdaptor.invoke(MethodAdaptor.java:103)
    at com.google.gwt.dev.shell.MethodDispatch.invoke(MethodDispatch.java:71)
    at com.google.gwt.dev.shell.OophmSessionHandler.invoke(OophmSessionHandler.java:172)
    at com.google.gwt.dev.shell.BrowserChannelServer.reactToMessages(BrowserChannelServer.java:293)
    at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:547)
    at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:364)
    at java.lang.Thread.run(Thread.java:662)
Caused by: com.google.gwt.user.client.rpc.SerializationException: com.google.appengine.api.datastore.Key/194261103
    at com.google.gwt.user.client.rpc.impl.SerializerBase.getTypeHandler(SerializerBase.java:153)
    at com.google.gwt.user.client.rpc.impl.SerializerBase.instantiate(SerializerBase.java:114)
    at com.google.gwt.user.client.rpc.impl.ClientSerializationStreamReader.deserialize(ClientSerializationStreamReader.java:396)
    at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamReader.readObject(AbstractSerializationStreamReader.java:119)
    at com.cbd.shared.entities.User_FieldSerializer.deserialize(User_FieldSerializer.java:117)
    at com.cbd.shared.entities.User_FieldSerializer.deserial(User_FieldSerializer.java:150)
    at com.google.gwt.user.client.rpc.impl.SerializerBase.deserialize(SerializerBase.java:95)
    at com.google.gwt.user.client.rpc.impl.ClientSerializationStreamReader.deserialize(ClientSerializationStreamReader.java:398)
    at com.google.gwt.user.client.rpc.impl.AbstractSerializationStreamReader.readObject(AbstractSerializationStreamReader.java:119)
    at com.google.gwt.user.client.rpc.impl.RequestCallbackAdapter$ResponseReader$8.read(RequestCallbackAdapter.java:106)
    at com.google.gwt.user.client.rpc.impl.RequestCallbackAdapter.onResponseReceived(RequestCallbackAdapter.java:214)
    ... 28 more