@Entity
@Table(name = DataBaseConstants.ANSWER_TABLE)
public class Answer extends Post<Long> {
   private static final long serialVersionUID = 639804536588328311L;

   @Id
   @GeneratedValue(strategy = GenerationType.IDENTITY)
   @Column(name = DataBaseConstants.ANSWER_ID, nullable = false, updatable = false, insertable = false)
   private Long answer_id;
   @ManyToOne(fetch = FetchType.LAZY, optional = false)
   @JoinColumn(name = "topic", referencedColumnName = "topic_id")
   private Topic topic;
   // @LazyToOne(LazyToOneOption.NO_PROXY)
   @ManyToOne(fetch = FetchType.LAZY, optional = false)
   @JoinColumn(name = "user", referencedColumnName = "user_id")
   private JuniorUser user;

   public Answer() {
   }

   public Answer(Long answer_id) {
      this.answer_id = answer_id;
   }

   public Answer(Long answer_id, Long version) {
      this.answer_id = answer_id;
      setVersion(version);
   }

   public Answer(Long answer_id, Integer rate, Date publish_date) {
      this.answer_id = answer_id;
      super.setRate(rate);
      super.setPublish_date(publish_date);
   }

   public Answer(String content, Integer rate, Date date) {
      super(content, rate, date);
   }

   public Long getAnswer_id() {
      return answer_id;
   }

   public void setAnswer_id(Long answer_id) {
      this.answer_id = answer_id;
   }

   @Transient
   @Override
   public Long getId() {
      return getAnswer_id();
   }

   public Topic getTopic() {
      return topic;
   }

   public void setTopic(Topic topic) {
                this.topic=topic;
   }

   public JuniorUser getUser() {
      return user;
   }
   public void setUser(JuniorUser user) {
      this.user = user;
   }
   @Override
   public String toString() {
      ToStringHelper helper = Objects.toStringHelper(getClass().getCanonicalName());
      helper.add("id", getId());
      helper.add("publish_date", getPublish_date());
      helper.add("rate", getRate());
      return helper.toString();
   }
}

java.lang.NullPointerException
   at org.hibernate.event.internal.DefaultFlushEntityEventListener.isUpdateNecessary(DefaultFlushEntityEventListener.java:240)
   at org.hibernate.event.internal.DefaultFlushEntityEventListener.onFlushEntity(DefaultFlushEntityEventListener.java:163)
   at org.hibernate.event.internal.AbstractFlushingEventListener.flushEntities(AbstractFlushingEventListener.java:227)
   at org.hibernate.event.internal.AbstractFlushingEventListener.flushEverythingToExecutions(AbstractFlushingEventListener.java:99)
   at org.hibernate.event.internal.DefaultFlushEventListener.onFlush(DefaultFlushEventListener.java:51)
   at org.hibernate.internal.SessionImpl.flush(SessionImpl.java:1233)
   at org.hibernate.internal.SessionImpl.managedFlush(SessionImpl.java:403)
   at org.hibernate.engine.transaction.internal.jdbc.JdbcTransaction.beforeTransactionCommit(JdbcTransaction.java:101)
   at org.hibernate.engine.transaction.spi.AbstractTransactionImpl.commit(AbstractTransactionImpl.java:175)
   at org.springframework.orm.hibernate4.HibernateTransactionManager.doCommit(HibernateTransactionManager.java:554)
   at org.springframework.transaction.support.AbstractPlatformTransactionManager.processCommit(AbstractPlatformTransactionManager.java:755)
   at org.springframework.transaction.support.AbstractPlatformTransactionManager.commit(AbstractPlatformTransactionManager.java:724)
   at org.springframework.transaction.interceptor.TransactionAspectSupport.commitTransactionAfterReturning(TransactionAspectSupport.java:475)
   at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:270)
   at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:94)
   at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
   at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:91)
   at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
   at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:631)
   at com.javahelp.service.AnswerService$$EnhancerByCGLIB$$be3aa647.delete(<generated>)
   at test.javahelp.dao.GenericServiceTest.doDelete(GenericServiceTest.java:235)
   at test.javahelp.dao.answer.AnswerServiceTestHibernate.testDelete(AnswerServiceTestHibernate.java:72)
   at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
   at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
   at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
   at java.lang.reflect.Method.invoke(Method.java:601)
   at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
   at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
   at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
   at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
   at org.springframework.test.context.junit4.statements.RunBeforeTestMethodCallbacks.evaluate(RunBeforeTestMethodCallbacks.java:74)
   at org.springframework.test.context.junit4.statements.RunAfterTestMethodCallbacks.evaluate(RunAfterTestMethodCallbacks.java:83)
   at org.springframework.test.context.junit4.statements.SpringRepeat.evaluate(SpringRepeat.java:72)
   at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:231)
   at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.runChild(SpringJUnit4ClassRunner.java:88)
   at org.junit.runners.ParentRunner$3.run(ParentRunner.java:193)
   at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:52)
   at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:191)
   at org.junit.runners.ParentRunner.access$000(ParentRunner.java:42)
   at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:184)
   at org.springframework.test.context.junit4.statements.RunBeforeTestClassCallbacks.evaluate(RunBeforeTestClassCallbacks.java:61)
   at org.springframework.test.context.junit4.statements.RunAfterTestClassCallbacks.evaluate(RunAfterTestClassCallbacks.java:71)
   at org.junit.runners.ParentRunner.run(ParentRunner.java:236)
   at org.springframework.test.context.junit4.SpringJUnit4ClassRunner.run(SpringJUnit4ClassRunner.java:174)
   at test.javahelp.dao.runner.GenericServiceTestRunner.run(GenericServiceTestRunner.java:29)
   at org.eclipse.jdt.internal.junit4.runner.JUnit4TestReference.run(JUnit4TestReference.java:50)
   at org.eclipse.jdt.internal.junit.runner.TestExecution.run(TestExecution.java:38)
   at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:467)
   at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.runTests(RemoteTestRunner.java:683)
   at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.run(RemoteTestRunner.java:390)
   at org.eclipse.jdt.internal.junit.runner.RemoteTestRunner.main(RemoteTestRunner.java:197)

public static FieldInterceptor extractFieldInterceptor(Object entity) {
      return ( FieldInterceptor ) ( ( FieldHandled ) entity ).getFieldHandler();
   }