Could not open Hibernate Session for transaction; nested exception is NPE

[momatej]

After migrating to Hibernate 4 and Spring 3.1 RC2: I getting following exception and I have no idea why:

Exception:

    org.springframework.transaction.CannotCreateTransactionException: Could not open Hibernate Session for transaction; nested exception is java.lang.NullPointerException
    org.springframework.orm.hibernate4.HibernateTransactionManager.doBegin(HibernateTransactionManager.java:428)
    ...

Logging:

 DEBUG Using SessionFactory 'sessionFactory' for OpenSessionInViewFilter
 DEBUG Opening Hibernate Session in OpenSessionInViewFilter
 DEBUG Found thread-bound Session [SessionImpl(PersistenceContext[entityKeys=[],collectionKeys=[]];ActionQueue[insertions=[] updates=[] deletions=[] collectionCreations=[] collectionRemovals=[] collectionUpdates=[]])] for Hibernate transaction
 DEBUG Creating new transaction with name [com.project.server.dao.hibernate.BalanceDAOHibernateImpl.getCurrentBalance]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT,readOnly; ''
 DEBUG txObject.getSessionHolder().getSession(: SessionImpl(PersistenceContext[entityKeys=[],collectionKeys=[]];ActionQueue[insertions=[] updates=[] deletions=[] collectionCreations=[] collectionRemovals=[] collectionUpdates=[]])
 DEBUG Preparing JDBC Connection of Hibernate Session [SessionImpl(PersistenceContext[entityKeys=[],collectionKeys=[]];ActionQueue[insertions=[] updates=[] deletions=[] collectionCreations=[] collectionRemovals=[] collectionUpdates=[]])]
 DEBUG SessionImpl(PersistenceContext[entityKeys=[],collectionKeys=[]];ActionQueue[insertions=[] updates=[] deletions=[] collectionCreations=[] collectionRemovals=[] collectionUpdates=[]])
 DEBUG Exposing Hibernate transaction as JDBC transaction [org.hibernate.engine.jdbc.internal.proxy.ConnectionProxyHandler@5620a822[valid=true]]
 DEBUG user: AbstractUser{id=30060, email='user@project.com', enabled=true}
 DEBUG ~~~~~~~~~~~~~~~~SESSION: SessionImpl(PersistenceContext[entityKeys=[],collectionKeys=[]];ActionQueue[insertions=[] updates=[] deletions=[] collectionCreations=[] collectionRemovals=[] collectionUpdates=[]])
 DEBUG ~~~~~~~~~~~~~~~~SESSION HOLDER session: SessionImpl(PersistenceContext[entityKeys=[],collectionKeys=[]];ActionQueue[insertions=[] updates=[] deletions=[] collectionCreations=[] collectionRemovals=[] collectionUpdates=[]])
 DEBUG BuyLaterQitem getByQitem createQuery list size: 1
 DEBUG user: AbstractUser{id=30060, email='user@project.com', enabled=true}
 DEBUG ~~~~~~~~~~~~~~~~SESSION: SessionImpl(PersistenceContext[entityKeys=[],collectionKeys=[]];ActionQueue[insertions=[] updates=[] deletions=[] collectionCreations=[] collectionRemovals=[] collectionUpdates=[]])
 DEBUG ~~~~~~~~~~~~~~~~SESSION HOLDER session: SessionImpl(PersistenceContext[entityKeys=[],collectionKeys=[]];ActionQueue[insertions=[] updates=[] deletions=[] collectionCreations=[] collectionRemovals=[] collectionUpdates=[]])
 DEBUG Initiating transaction commit
 DEBUG Committing Hibernate transaction on Session [SessionImpl(PersistenceContext[entityKeys=[],collectionKeys=[]];ActionQueue[insertions=[] updates=[] deletions=[] collectionCreations=[] collectionRemovals=[] collectionUpdates=[]])]
 DEBUG Not closing pre-bound Hibernate Session [SessionImpl(PersistenceContext[entityKeys=[],collectionKeys=[]];ActionQueue[insertions=[] updates=[] deletions=[] collectionCreations=[] collectionRemovals=[] collectionUpdates=[]])] after transaction
 DEBUG Found thread-bound Session [null] for Hibernate transaction
 DEBUG Creating new transaction with name [com.project.server.dao.hibernate.BalanceDAOHibernateImpl.getCurrentBalance]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT,readOnly; ''
 DEBUG txObject.getSessionHolder().getSession(: null
 DEBUG Preparing JDBC Connection of Hibernate Session [null]
 DEBUG 
 DERROR java.lang.NullPointerException
	at org.springframework.orm.hibernate4.HibernateTransactionManager.doBegin(HibernateTransactionManager.java:330)
 DEBUG Closing Hibernate Session in OpenSessionInViewFilter

Application context:

       
 <bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource" destroy-method="close">
            <property name="driverClass" value="${jdbc.driverClass}"/>
            <property name="jdbcUrl" value="${jdbc.url}"/>
            <property name="user" value="${env.jdbc.user}"/>
            <property name="password" value="${env.jdbc.password}"/>
            <property name="testConnectionOnCheckin" value="true"/>
            <property name="testConnectionOnCheckout" value="true"/>
        </bean>
            <bean class="org.springframework.orm.hibernate4.HibernateExceptionTranslator"/>
            <bean id="sessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
            <property name="dataSource" ref="dataSource"/>
                <property name="packagesToScan">
                <list>
                    <value>com.project.server.dao.hibernate</value>
                    <value>com.project.server.service.impl</value>
                    <value>com.project.server.service.handler</value>
                    <value>com.project.server.service.schedule</value>
                    <value>com.project.server.service.gateway.impl</value>
                </list>
            </property>
                <property name="mappingResources">
                <list>
                    <value>com/project/server/domain/AdminApplication.hbm.xml</value>
                    ...   
                </list>
            </property>
            <property name="hibernateProperties">
                <props>
                    <prop key="hibernate.dialect">${db.dialect}</prop>
                    <prop key="hibernate.show_sql">false</prop>
                    <prop key="hibernate.format_sql">false</prop>
                    <prop key="hibernate.use_sql_comments">false</prop>
                    <prop key="hibernate.max_fetch_depth">1</prop>
                    <prop key="hibernate.cache.use_structured_entries">false</prop>
                    <prop key="hibernate.bytecode.use_reflection_optimizer">false</prop>
                    <prop key="hibernate.jdbc.batch_size">100</prop>
                    <prop key="hibernate.generate_statistics">false</prop>
                    <prop key="hibernate.cache.use_query_cache">true</prop>
                    <prop key="hibernate.cache.use_second_level_cache">true</prop>
                    <prop key="hibernate.cache.use_minimal_puts">true</prop>
                    <prop key="hibernate.cache.region.factory_class">org.hibernate.cache.ehcache.SingletonEhCacheRegionFactory</prop>
                    <prop key="hibernate.cache.provider_class">org.hibernate.cache.EhCacheProvider</prop>

                        <!--hibernate search -->
                    <prop key="hibernate.search.default.directory_provider">org.hibernate.search.store.impl.FSDirectoryProvider</prop>
                    <prop key="hibernate.search.default.indexBase">${server.compass.repo}</prop>
                    <prop key="hibernate.search.default.batch.merge_factor">3</prop>
                    <prop key="hibernate.search.id.new_generator_mappings">true</prop>
                    <prop key="hibernate.search.default.optimizer.operation_limit.max">1000</prop>
                    <prop key="hibernate.search.default.optimizer.transaction_limit.max">100</prop>
                    <prop key="hibernate.search.reader.strategy">not-shared</prop>
                    <prop key="hibernate.search.worker.execution">async</prop>
                    <prop key="hibernate.search.worker.thread_pool.size">20</prop>
                    <prop key="hibernate.search.worker.buffer_queue.max">100</prop>
                        <prop key="max_fetch_depth">1</prop>
        
                </props>
            </property>
        </bean>
            <tx:annotation-driven/>
            <bean id="txManager" class="org.springframework.orm.hibernate4.HibernateTransactionManager">
            <property name="sessionFactory" ref="sessionFactory"/>
           <!-- <property name="hibernateManagedSession" value="false"/> -->
            </bean>
            <tx:advice id="txAdvice" transaction-manager="txManager">
            <tx:attributes>
                <tx:method name="get*" read-only="true"/>
                <tx:method name="*"/>
            </tx:attributes>
        </tx:advice>
            <aop:config>
            <aop:pointcut id="loadableActionOperation" expression="execution(* com.project.server.domain.LoadableAction.*(..))"/>
            <aop:advisor advice-ref="txAdvice" pointcut-ref="loadableActionOperation"/>
        </aop:config>

After little source code digging it seems that this the NullPointer Culprit (line# 342):

org.springframework.orm.hibernate4.HibernateTransactionManager (@author Juergen Hoeller) :

          session = txObject.getSessionHolder().getSession();

337     if (this.prepareConnection && isSameConnectionForEntireSession(session)) {
		// We're allowed to change the transaction settings of the JDBC Connection.
		if (logger.isDebugEnabled()) {
		logger.debug("Preparing JDBC Connection of Hibernate Session [" + session + "]");
		}
342     Connection con = ((SessionImplementor) session).connection();
	  Integer previousIsolationLevel = DataSourceUtils.prepareConnectionForTransaction(con, definition);
	  txObject.setPreviousIsolationLevel(previousIsolationLevel);
345	  }

Can someone explain to me why

txObject.getSessionHolder().getSession();

would return null even though the session seems to exist according to the log?