提交出现异常

java.lang.IllegalArgumentException: attempt to create saveOrUpdate event with null entity
org.hibernate.event.SaveOrUpdateEvent.<init>(SaveOrUpdateEvent.java:63)
org.hibernate.event.SaveOrUpdateEvent.<init>(SaveOrUpdateEvent.java:46)
org.hibernate.impl.SessionImpl.save(SessionImpl.java:551)
org.hibernate.impl.SessionImpl.save(SessionImpl.java:547)
org.springframework.orm.hibernate3.HibernateTemplate$12.doInHibernate(HibernateTemplate.java:722)
org.springframework.orm.hibernate3.HibernateTemplate$12.doInHibernate(HibernateTemplate.java:718)
org.springframework.orm.hibernate3.HibernateTemplate.doExecute(HibernateTemplate.java:411)
org.springframework.orm.hibernate3.HibernateTemplate.executeWithNativeSession(HibernateTemplate.java:379)
org.springframework.orm.hibernate3.HibernateTemplate.save(HibernateTemplate.java:718)
cn.muke.ssh.dao.ProductDao.save(ProductDao.java:15)
cn.muke.ssh.service.ProductService.save(ProductService.java:24)
cn.muke.ssh.service.ProductService$$FastClassByCGLIB$$6511f0ce.invoke(<generated>)
org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204)
org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:698)
org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:150)
org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:110)
org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:172)
org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:631)
cn.muke.ssh.service.ProductService$$EnhancerByCGLIB$$685eaafc.save(<generated>)
cn.muke.ssh.action.ProductAction.save(ProductAction.java:27)
sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
java.lang.reflect.Method.invoke(Method.java:483)
ognl.OgnlRuntime.invokeMethod(OgnlRuntime.java:891)
ognl.OgnlRuntime.callAppropriateMethod(OgnlRuntime.java:1293)
ognl.ObjectMethodAccessor.callMethod(ObjectMethodAccessor.java:68)
com.opensymphony.xwork2.ognl.accessor.XWorkMethodAccessor.callMethodWithDebugInfo(XWorkMethodAccessor.java:117)
com.opensymphony.xwork2.ognl.accessor.XWorkMethodAccessor.callMethod(XWorkMethodAccessor.java:108)
ognl.OgnlRuntime.callMethod(OgnlRuntime.java:1369)
ognl.ASTMethod.getValueBody(ASTMethod.java:90)
ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:212)
ognl.SimpleNode.getValue(SimpleNode.java:258)
ognl.Ognl.getValue(Ognl.java:494)
ognl.Ognl.getValue(Ognl.java:458)
com.opensymphony.xwork2.ognl.OgnlUtil$2.execute(OgnlUtil.java:309)
com.opensymphony.xwork2.ognl.OgnlUtil.compileAndExecute(OgnlUtil.java:340)
com.opensymphony.xwork2.ognl.OgnlUtil.getValue(OgnlUtil.java:307)
com.opensymphony.xwork2.DefaultActionInvocation.invokeAction(DefaultActionInvocation.java:423)
com.opensymphony.xwork2.DefaultActionInvocation.invokeActionOnly(DefaultActionInvocation.java:287)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:250)
org.apache.struts2.interceptor.DeprecationInterceptor.intercept(DeprecationInterceptor.java:41)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
org.apache.struts2.interceptor.debugging.DebuggingInterceptor.intercept(DebuggingInterceptor.java:256)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.DefaultWorkflowInterceptor.doIntercept(DefaultWorkflowInterceptor.java:167)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.validator.ValidationInterceptor.doIntercept(ValidationInterceptor.java:265)
org.apache.struts2.interceptor.validation.AnnotationValidationInterceptor.doIntercept(AnnotationValidationInterceptor.java:76)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.ConversionErrorInterceptor.intercept(ConversionErrorInterceptor.java:138)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:229)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.ParametersInterceptor.doIntercept(ParametersInterceptor.java:229)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.StaticParametersInterceptor.intercept(StaticParametersInterceptor.java:191)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
org.apache.struts2.interceptor.MultiselectInterceptor.intercept(MultiselectInterceptor.java:73)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
org.apache.struts2.interceptor.DateTextFieldInterceptor.intercept(DateTextFieldInterceptor.java:125)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
org.apache.struts2.interceptor.CheckboxInterceptor.intercept(CheckboxInterceptor.java:91)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
org.apache.struts2.interceptor.FileUploadInterceptor.intercept(FileUploadInterceptor.java:253)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.ModelDrivenInterceptor.intercept(ModelDrivenInterceptor.java:100)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.ScopedModelDrivenInterceptor.intercept(ScopedModelDrivenInterceptor.java:141)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.ChainingInterceptor.intercept(ChainingInterceptor.java:145)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.PrepareInterceptor.doIntercept(PrepareInterceptor.java:171)
com.opensymphony.xwork2.interceptor.MethodFilterInterceptor.intercept(MethodFilterInterceptor.java:98)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.I18nInterceptor.intercept(I18nInterceptor.java:139)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
org.apache.struts2.interceptor.ServletConfigInterceptor.intercept(ServletConfigInterceptor.java:164)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.AliasInterceptor.intercept(AliasInterceptor.java:193)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
com.opensymphony.xwork2.interceptor.ExceptionMappingInterceptor.intercept(ExceptionMappingInterceptor.java:189)
com.opensymphony.xwork2.DefaultActionInvocation.invoke(DefaultActionInvocation.java:244)
org.apache.struts2.impl.StrutsActionProxy.execute(StrutsActionProxy.java:54)
org.apache.struts2.dispatcher.Dispatcher.serviceAction(Dispatcher.java:564)
org.apache.struts2.dispatcher.ng.ExecuteOperations.executeAction(ExecuteOperations.java:81)
org.apache.struts2.dispatcher.ng.filter.StrutsPrepareAndExecuteFilter.doFilter(StrutsPrepareAndExecuteFilter.java:99)

代码：

package cn.muke.ssh.action;

import com.opensymphony.xwork2.ActionSupport;

import com.opensymphony.xwork2.ModelDriven;

import cn.muke.ssh.domain.Product;

import cn.muke.ssh.service.ProductService;

public class ProductAction extends ActionSupport implements ModelDriven<Product> {

private static final long serialVersionUID = 1L;

//模型驱动使用的类

private Product product;

public Product getModel() {

// TODO Auto-generated method stub

return product;

}

//Struts和Spring整合过程中按名称自动注入的业务层的类

private ProductService productService;

public void setProductService(ProductService productService) {

this.productService = productService;

}

   //保存商品的执行方法

public String save(){

System.out.println("Action中的save方法执行了！");

productService.save(product);

return NONE;

}

applicationContext：

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

xmlns:context="http://www.springframework.org/schema/context"

xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx"

xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p"

xsi:schemaLocation="http://www.springframework.org/schema/beans 

    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd

    http://www.springframework.org/schema/context

    http://www.springframework.org/schema/context/spring-context-3.0.xsd

    http://www.springframework.org/schema/aop

    http://www.springframework.org/schema/aop/spring-aop-3.0.xsd

    http://www.springframework.org/schema/tx

    http://www.springframework.org/schema/tx/spring-tx-3.0.xsd">

    <!-- 引入外部的属性文件 -->

    <context:property-placeholder location="classpath:jdbc.properties"/>

    <!-- 配置连接池 -->

    <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">

        <property name="driverClass" value="${jdbc.driverClass}"/>

        <property name="jdbcUrl" value="${jdbc.url}"/>

        <property name="user" value="${jdbc.username}"/>

        <property name="password" value="${jdbc.password}"/>

    </bean>

    <!-- 配置Hibernate的相关属性 -->

    <bean id="sessionFactory" class="org.springframework.orm.hibernate3.LocalSessionFactoryBean">

          <!-- 注入连接池 -->

          <property name="dataSource" ref="dataSource"/>

          <!-- 配置Hibernate的属性 -->

          <property name="hibernateProperties">

             <props>

                   <prop key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop>

                   <prop key="hibernate.show_sql">true</prop>

                   <prop key="hibernate.format_sql">true</prop>

                   <prop key="hibernate.hbm2ddl.auto">update</prop>

             </props>

          </property>

          <!-- 加载Hibernate的映射文件 -->

          <property name="mappingResources">

                   <list>

                        <value>cn/muke/ssh/domain/Product.hbm.xml</value> 

                   </list>

          </property>

    </bean>

    <!-- 配置Action的类 -->

    <bean id="productAction" class="cn.muke.ssh.action.ProductAction" scope="prototype">

            <!-- 手动注入Service -->

            <property name="productService" ref="productService"></property>

    </bean>

    <!-- 配置业务层的类 -->

    <bean id="productService" class="cn.muke.ssh.service.ProductService">

            <property name="productDao" ref="productDao"></property>

    </bean>

    <!-- 配置DAO的类 -->

    <bean id="productDao" class="cn.muke.ssh.dao.ProductDao">

            <property name="sessionFactory" ref="sessionFactory"></property>

    </bean>

    <!-- 配置事务管理器 -->

    <bean id="transactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager">

            <property name="sessionFactory" ref="sessionFactory"></property>

    </bean>

    <!--开启注解事务 -->

    <tx:annotation-driven transaction-manager="transactionManager"/>

 </beans>

struts.xml:

<?xml version="1.0" encoding="UTF-8" ?>

<!DOCTYPE struts PUBLIC "-//Apache Software Foundation//DTD Struts Configuration 2.1//EN" 

"http://struts.apache.org/dtds/struts-2.1.dtd">

<struts>

      <package name="ssh" extends="struts-default" namespace="/">

            <action name="product_*" class="productAction" method="{1}"></action>

      </package>

</struts>