Hibernate异常：IllegalArgumentException

异常信息：

 java.lang.IllegalArgumentException: attempt to create delete event with null entity
     at org.hibernate.event.spi.DeleteEvent.<init>(DeleteEvent.java:31)
     at org.hibernate.internal.SessionImpl.delete(SessionImpl.java:860)
     at com.geore.test.TestDemo4.fun2(TestDemo4.java:77)
     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.junit.runners.ParentRunner.runLeaf(ParentRunner.java:263)
     at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:69)
     at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:48)
     at org.junit.runners.ParentRunner$3.run(ParentRunner.java:231)
     at org.junit.runners.ParentRunner$1.schedule(ParentRunner.java:60)
     at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:229)
     at org.junit.runners.ParentRunner.access$000(ParentRunner.java:50)
     at org.junit.runners.ParentRunner$2.evaluate(ParentRunner.java:222)
     at org.junit.runners.ParentRunner.run(ParentRunner.java:292)
     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)

错误代码：

 // 第一步：查找用戶
    Users user = session.get(Users.class, "4028d4015e6ebff8015e6ebffffd0004");
    session.delete(user);

异常原因：

　　从异常信息的显示来看，很容易看出来产生异常的原因，是因为存在null对象，切这个对象在调用Hibernate的Session类的delete()方法。那么很显然user对象为空，Hibernate没有通过get()方法查找到Users对象。那么这个原因就是处在给的查询条件是不存在的，因此是id在数据库中不存在，因此找不到此条记录，因此出现异常。将id改成一个存在的值即可。

正确的解决代码：

 // 第一步：查找用戶
     Users user = session.get(Users.class, "4028d4015e6ebff8015e6ebfffa60000");
     session.delete(user);