что не так с моим классом сущности

Question

Это мой код для использования класса сущности с использованием локатора в GWT

    @SuppressWarnings("unchecked")
public List<User> findAllUsers() {
    EntityManager em = HibernateUtil.getManager();

    try {
    //          userList = em.createQuery("from User").getResultList();
    //          Query query = em.createNativeQuery("select * from User");
    //          System.out.println("query is created!");
    //          List<User> userList = query.getResultList();

                List<User> userList = new ArrayList<User>(em.createNativeQuery("select * from User").getResultList());
                // force it to materialize
                System.out.println(userList.size());
                return userList;
            }catch(Exception e){
                e.printStackTrace();
            } 
            finally {
                // em.close();
            }
            System.out.println("server is null");
            return null;
        }

Код моей сущности здесь:

@Entity
@Table(name = "user")
public class User implements Serializable{


    /**
     * 
     */
    private static final long serialVersionUID = 1L;

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

@Version
    @Column(name = "version")
private Integer version;

private String userName;
private String password;
private String copyPassword;
private String qqNum;
private String mailAddress;
private String selfment;

private User superVisor;

public Long getId() {
    return this.id;
}

public static long getSerialversionuid() {
    return serialVersionUID;
}

public void setId(Long id) {
    this.id = id;
}

public void setVersion(Integer version) {
    this.version = version;
}

public Integer getVersion() {
    return this.version;
}

public String getUserName() {
    return this.userName;
}
public void setUserName(String userName) {
    this.userName = userName;
}
public String getPassword() {
    return this.password;
}
public void setPassword(String password) {
    this.password = password;
}
public String getCopyPassword() {
    return this.copyPassword;
}
public void setCopyPassword(String copyPassword) {
    this.copyPassword = copyPassword;
}
public String getQqNum() {
    return this.qqNum;
}
public void setQqNum(String qqNum) {
    this.qqNum = qqNum;
}
public String getMailAddress() {
    return this.mailAddress;
}
public void setMailAddress(String mailAddress) {
    this.mailAddress = mailAddress;
}
public String getSelfment() {
    return this.selfment;
}
public void setSelfment(String selfment) {
    this.selfment = selfment;
}

public void setSuperVisor(User superVisor)  {
    this.superVisor = superVisor;
}
public User getSuperVisor() {
    return this.superVisor;
    }


}

ничего в консоли, и эта информация очень скоро появилась в режиме разработки:

Caused by: java.lang.RuntimeException: Server Error: NONE
    at com.google.web.bindery.requestfactory.shared.Receiver.onFailure(Receiver.java:44)
    at com.google.web.bindery.requestfactory.shared.impl.AbstractRequest.onFail(AbstractRequest.java:118)
    at com.google.web.bindery.requestfactory.shared.impl.AbstractRequestContext$StandardPayloadDialect.processPayload(AbstractRequestContext.java:359)
    at com.google.web.bindery.requestfactory.shared.impl.AbstractRequestContext$5.onTransportSuccess(AbstractRequestContext.java:1108)
    at com.google.web.bindery.requestfactory.gwt.client.DefaultRequestTransport$1.onResponseReceived(DefaultRequestTransport.java:136)
    at com.google.gwt.http.client.Request.fireOnResponseReceived(Request.java:287)
    at com.google.gwt.http.client.RequestBuilder$1.onReadyStateChange(RequestBuilder.java:395)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    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:337)
    at com.google.gwt.dev.shell.BrowserChannelServer.invokeJavascript(BrowserChannelServer.java:218)
    at com.google.gwt.dev.shell.ModuleSpaceOOPHM.doInvoke(ModuleSpaceOOPHM.java:136)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNative(ModuleSpace.java:561)
    at com.google.gwt.dev.shell.ModuleSpace.invokeNativeObject(ModuleSpace.java:269)
    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:213)
    at sun.reflect.GeneratedMethodAccessor25.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
    at java.lang.reflect.Method.invoke(Unknown Source)
    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:292)
    at com.google.gwt.dev.shell.BrowserChannelServer.processConnection(BrowserChannelServer.java:546)
    at com.google.gwt.dev.shell.BrowserChannelServer.run(BrowserChannelServer.java:363)
    at java.lang.Thread.run(Unknown Source)

Кто-нибудь может подсказать, почему возникает эта ошибка?