整合ssh时报错：Messages: attempt to create saveOrUpdate event with null entity

<struts>
 
    <constant name="struts.devMode" value="true" />
    <constant name="struts.i18n.encoding" value="UTF-8"/>
    <constant name="struts.ui.theme" value="simple"></constant>
     
    <constant name="struts.objectFactory" value="spring"/>
 
    <package name="user" namespace="/user" extends="struts-default">
        <action name="userAction" class="userAction">
            <result name="SUCCESS">/list.jsp</result>
            <result name="ERROR">/error.jsp</result>
        </action>
    </package>
 
</struts>

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
    xmlns:aop="http://www.springframework.org/schema/aop" xmlns:tx="http://www.springframework.org/schema/tx"
    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
">
    <bean name="userAction" class="cn.xiaoxing.s3.action.UserAction" scope="prototype">
        <property name="userEbi" ref="userEbi"></property>
    </bean>
    <bean name="userEbi" class="cn.xiaoxing.s3.business.ebo.UserEbo">
        <property name="userDao" ref="S3Impl"></property>
    </bean>
     
    <bean name="S3Impl" class="cn.xiaoxing.s3.dao.impl.S3Impl">
        <!-- ref="dbConfig"：表示要注意哪个对象 -->
        <property name="sessionFactory" ref="hbConfig"></property>
    </bean>
     
    <!-- 在Spring的application context中创建 SessionFactory -->
    <bean id="hbConfig" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
        <!-- 把连接数据信息注入到dbConfig -->
        <property name="dataSource" ref="dataSource"></property>
         
        <!-- 资源注册 -->
        <property name="mappingResources">
            <list>
                <value>cn/xiaoxing/s3/vo/UserModel.hbm.xml</value>
            </list>
        </property>
         
        <!-- 可选配置 -->
        <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.current_session_context_class">org.springframework.orm.hibernate4.SpringSessionContext</prop>
            </props>
        </property>
    </bean>
 
    <!-- 配置数据源 -->
    <bean name="dataSource" class="org.apache.commons.dbcp.BasicDataSource">
        <property name="driverClassName">
            <value>com.mysql.jdbc.Driver</value>
        </property>
        <property name="url">
            <value>jdbc:mysql://localhost:3306/test?useUnicode=true&amp;characterEncoding=UTF-8</value>
        </property>
        <property name="username" value="root"></property>
        <property name="password" value="123456"></property>
    </bean>
     
    <!-- 第二种方法：spring事务配置，拟管理类上需要加上@transactional支持 
    <bean id="txManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager"> 
        <property name="dataSource" ref="dataSource"/>
    </bean>
    <tx:annotation-driven transaction-manager="txManager"/>
    -->
     
    <!-- 第一种方法：spring事务配置    -->
    <bean id="txManager" class="org.springframework.orm.hibernate4.HibernateTransactionManager"> 
        <property name="sessionFactory" ref="hbConfig"></property>
    </bean> 
    <!--事务切入点配置-->
    <tx:advice id="txAdvice" transaction-manager="txManager">
        <tx:attributes>
            <tx:method name="get*" read-only="true" />
            <tx:method name="*" />
        </tx:attributes>
    </tx:advice>
    <!--配置切入点与被应用类关联-->
    <aop:config>
        <aop:pointcut id="myPointCut" expression="execution(* cn.xiaoxing.s3..*.*(..))"/>
        <aop:advisor advice-ref="txAdvice" pointcut-ref="myPointCut"/>
    </aop:config>
     
     
</beans>