java.lang.IllegalArgumentException 求解
java.lang.IllegalArgumentException: attempt to create merge event with null entity 
  org.hibernate.event.MergeEvent.(MergeEvent.java:60)
  org.hibernate.event.MergeEvent.(MergeEvent.java:43)
  org.hibernate.impl.SessionImpl.merge(SessionImpl.java:689)
  org.hibernate.impl.SessionImpl.merge(SessionImpl.java:693)
  org.springframework.orm.hibernate3.HibernateTemplate$23.doInHibernate(HibernateTemplate.java:827)
  org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:419)
  org.springframework.orm.hibernate3.HibernateTemplate.executeWithNativeSession(HibernateTemplate.java:374)
  org.springframework.orm.hibernate3.HibernateTemplate.merge(HibernateTemplate.java:824)
  com.lqkj.prs.dao.impl.BaseDAOSupport.merge(BaseDAOSupport.java:74)
  com.lqkj.prs.service.impl.QuestionnaireWlyxyyqkServiceImpl.merge(QuestionnaireWlyxyyqkServiceImpl.java:36)
  sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
  sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
  java.lang.reflect.Method.invoke(Method.java:597)
  org.springframework.aop.support.AopUtils.invokeJoinpointUsingReflection(AopUtils.java:307)
  org.springframework.aop.framework.ReflectiveMethodInvocation.invokeJoinpoint(ReflectiveMethodInvocation.java:182)
  org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:149)
  org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:106)
  org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
  org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:89)
  org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:171)
  org.springframework.aop.framework.JdkDynamicAopProxy.invoke(JdkDynamicAopProxy.java:204)
  $Proxy31.merge(Unknown Source)
  com.lqkj.prs.action.QuestionnaireWlyxyyqkAction.save(QuestionnaireWlyxyyqkAction.java:66)
  sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
  sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
  sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
  java.lang.reflect.Method.invoke(Method.java:597)
  com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:441)
  com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:280)
  com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:243)
  com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:165)
  com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:87)
  com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:237)
  com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:252)
  org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.