An unexpected error occured

The bean encountered a non-application exception; nested exception is: javax.persistence.PersistenceException: org.hibernate.exception.ConstraintViolationException: Column 'user_id' cannot be null
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com.commafeed.frontend.utils.exception.DisplayException: The bean encountered a non-application exception; nested exception is:
	javax.persistence.PersistenceException: org.hibernate.exception.ConstraintViolationException: Column 'user_id' cannot be null
	at com.commafeed.frontend.pages.GoogleImportCallbackPage.<init>(GoogleImportCallbackPage.java:94)
	at sun.reflect.GeneratedConstructorAccessor187.newInstance(Unknown Source)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:525)
	at org.apache.wicket.session.DefaultPageFactory.newPage(DefaultPageFactory.java:170)
	at org.apache.wicket.session.DefaultPageFactory.newPage(DefaultPageFactory.java:98)
	at org.apache.wicket.DefaultMapperContext.newPageInstance(DefaultMapperContext.java:137)
	at org.apache.wicket.core.request.handler.PageProvider.resolvePageInstance(PageProvider.java:278)
	at org.apache.wicket.core.request.handler.PageProvider.getPageInstance(PageProvider.java:166)
	at org.apache.wicket.request.handler.render.PageRenderer.getPage(PageRenderer.java:78)
	at org.apache.wicket.request.handler.render.WebPageRenderer.renderPage(WebPageRenderer.java:94)
	at org.apache.wicket.request.handler.render.WebPageRenderer.respond(WebPageRenderer.java:244)
	at org.apache.wicket.core.request.handler.RenderPageRequestHandler.respond(RenderPageRequestHandler.java:165)
	at org.apache.wicket.request.cycle.RequestCycle$HandlerExecutor.respond(RequestCycle.java:840)
	at org.apache.wicket.request.RequestHandlerStack.execute(RequestHandlerStack.java:64)
	at org.apache.wicket.request.cycle.RequestCycle.execute(RequestCycle.java:254)
	at org.apache.wicket.request.cycle.RequestCycle.processRequest(RequestCycle.java:211)
	at org.apache.wicket.request.cycle.RequestCycle.processRequestAndDetach(RequestCycle.java:282)
	at org.apache.wicket.protocol.http.WicketFilter.processRequestCycle(WicketFilter.java:244)
	at org.apache.wicket.protocol.http.WicketFilter.processRequest(WicketFilter.java:188)
	at org.apache.wicket.protocol.http.WicketFilter.doFilter(WicketFilter.java:267)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
	at org.apache.tomee.catalina.OpenEJBValve.invoke(OpenEJBValve.java:45)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
	at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
	at java.lang.Thread.run(Thread.java:722)
Caused by: javax.ejb.EJBException: The bean encountered a non-application exception; nested exception is:
	javax.persistence.PersistenceException: org.hibernate.exception.ConstraintViolationException: Column 'user_id' cannot be null
	at org.apache.openejb.core.ivm.BaseEjbProxyHandler.convertException(BaseEjbProxyHandler.java:363)
	at org.apache.openejb.core.ivm.BaseEjbProxyHandler.invoke(BaseEjbProxyHandler.java:283)
	at com.commafeed.backend.dao.FeedCategoryDAO$LocalBeanProxy.save(com/commafeed/backend/dao/FeedCategoryDAO.java)
	at com.commafeed.backend.feeds.OPMLImporter.handleOutline(OPMLImporter.java:49)
	at com.commafeed.backend.feeds.OPMLImporter.importOpml(OPMLImporter.java:34)
	at com.commafeed.frontend.pages.GoogleImportCallbackPage.<init>(GoogleImportCallbackPage.java:92)
	... 37 more
Caused by: javax.persistence.PersistenceException: org.hibernate.exception.ConstraintViolationException: Column 'user_id' cannot be null
	at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1387)
	at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1310)
	at org.hibernate.ejb.AbstractEntityManagerImpl.convert(AbstractEntityManagerImpl.java:1316)
	at org.hibernate.ejb.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:881)
	at org.apache.openejb.persistence.JtaEntityManager.persist(JtaEntityManager.java:126)
	at com.commafeed.backend.dao.GenericDAO.save(GenericDAO.java:39)
	at sun.reflect.GeneratedMethodAccessor152.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:601)
	at org.apache.openejb.core.interceptor.ReflectionInvocationContext$Invocation.invoke(ReflectionInvocationContext.java:181)
	at org.apache.openejb.core.interceptor.ReflectionInvocationContext.proceed(ReflectionInvocationContext.java:163)
	at org.apache.openejb.cdi.CdiInterceptor.invoke(CdiInterceptor.java:130)
	at org.apache.openejb.cdi.CdiInterceptor.access$000(CdiInterceptor.java:43)
	at org.apache.openejb.cdi.CdiInterceptor$1.call(CdiInterceptor.java:67)
	at org.apache.openejb.cdi.CdiInterceptor.aroundInvoke(CdiInterceptor.java:73)
	at sun.reflect.GeneratedMethodAccessor32.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:601)
	at org.apache.openejb.core.interceptor.ReflectionInvocationContext$Invocation.invoke(ReflectionInvocationContext.java:181)
	at org.apache.openejb.core.interceptor.ReflectionInvocationContext.proceed(ReflectionInvocationContext.java:163)
	at org.apache.openejb.monitoring.StatsInterceptor.record(StatsInterceptor.java:180)
	at org.apache.openejb.monitoring.StatsInterceptor.invoke(StatsInterceptor.java:99)
	at sun.reflect.GeneratedMethodAccessor31.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:601)
	at org.apache.openejb.core.interceptor.ReflectionInvocationContext$Invocation.invoke(ReflectionInvocationContext.java:181)
	at org.apache.openejb.core.interceptor.ReflectionInvocationContext.proceed(ReflectionInvocationContext.java:163)
	at org.apache.openejb.core.interceptor.InterceptorStack.invoke(InterceptorStack.java:138)
	at org.apache.openejb.core.stateless.StatelessContainer._invoke(StatelessContainer.java:239)
	at org.apache.openejb.core.stateless.StatelessContainer.invoke(StatelessContainer.java:191)
	at org.apache.openejb.core.ivm.EjbObjectProxyHandler.synchronizedBusinessMethod(EjbObjectProxyHandler.java:256)
	at org.apache.openejb.core.ivm.EjbObjectProxyHandler.businessMethod(EjbObjectProxyHandler.java:251)
	at org.apache.openejb.core.ivm.EjbObjectProxyHandler._invoke(EjbObjectProxyHandler.java:85)
	at org.apache.openejb.core.ivm.BaseEjbProxyHandler.invoke(BaseEjbProxyHandler.java:279)
	... 41 more
Caused by: org.hibernate.exception.ConstraintViolationException: Column 'user_id' cannot be null
	at org.hibernate.exception.internal.SQLExceptionTypeDelegate.convert(SQLExceptionTypeDelegate.java:74)
	at org.hibernate.exception.internal.StandardSQLExceptionConverter.convert(StandardSQLExceptionConverter.java:49)
	at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:125)
	at org.hibernate.engine.jdbc.spi.SqlExceptionHelper.convert(SqlExceptionHelper.java:110)
	at org.hibernate.engine.jdbc.internal.proxy.AbstractStatementProxyHandler.continueInvocation(AbstractStatementProxyHandler.java:129)
	at org.hibernate.engine.jdbc.internal.proxy.AbstractProxyHandler.invoke(AbstractProxyHandler.java:81)
	at $Proxy113.executeUpdate(Unknown Source)
	at org.hibernate.id.IdentityGenerator$GetGeneratedKeysDelegate.executeAndExtract(IdentityGenerator.java:96)
	at org.hibernate.id.insert.AbstractReturningDelegate.performInsert(AbstractReturningDelegate.java:58)
	at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:2936)
	at org.hibernate.persister.entity.AbstractEntityPersister.insert(AbstractEntityPersister.java:3447)
	at org.hibernate.action.internal.EntityIdentityInsertAction.execute(EntityIdentityInsertAction.java:81)
	at org.hibernate.engine.spi.ActionQueue.execute(ActionQueue.java:362)
	at org.hibernate.engine.spi.ActionQueue.addResolvedEntityInsertAction(ActionQueue.java:203)
	at org.hibernate.engine.spi.ActionQueue.addInsertAction(ActionQueue.java:183)
	at org.hibernate.engine.spi.ActionQueue.addAction(ActionQueue.java:167)
	at org.hibernate.event.internal.AbstractSaveEventListener.addInsertAction(AbstractSaveEventListener.java:321)
	at org.hibernate.event.internal.AbstractSaveEventListener.performSaveOrReplicate(AbstractSaveEventListener.java:286)
	at org.hibernate.event.internal.AbstractSaveEventListener.performSave(AbstractSaveEventListener.java:192)
	at org.hibernate.event.internal.AbstractSaveEventListener.saveWithGeneratedId(AbstractSaveEventListener.java:125)
	at org.hibernate.ejb.event.EJB3PersistEventListener.saveWithGeneratedId(EJB3PersistEventListener.java:78)
	at org.hibernate.event.internal.DefaultPersistEventListener.entityIsTransient(DefaultPersistEventListener.java:208)
	at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:151)
	at org.hibernate.event.internal.DefaultPersistEventListener.onPersist(DefaultPersistEventListener.java:78)
	at org.hibernate.internal.SessionImpl.firePersist(SessionImpl.java:843)
	at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:818)
	at org.hibernate.internal.SessionImpl.persist(SessionImpl.java:822)
	at org.hibernate.ejb.AbstractEntityManagerImpl.persist(AbstractEntityManagerImpl.java:875)
	... 71 more
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Column 'user_id' cannot be null
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.lang.reflect.Constructor.newInstance(Constructor.java:525)
	at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
	at com.mysql.jdbc.Util.getInstance(Util.java:386)
	at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1041)
	at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4120)
	at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4052)
	at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2503)
	at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2664)
	at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2815)
	at com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2155)
	at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2458)
	at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2375)
	at com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2359)
	at sun.reflect.GeneratedMethodAccessor48.invoke(Unknown Source)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:601)
	at org.hibernate.engine.jdbc.internal.proxy.AbstractStatementProxyHandler.continueInvocation(AbstractStatementProxyHandler.java:122)
	... 94 more