我在日志中收到以下异常，不知道我错过了什么？ 以下是我从日志中提取的信息
2015.09.17 18:43:11 INFO web[o.s.s.n.NotificationService] Notification service started (delay 60 sec.)
2015.09.17 18:43:11 INFO web[o.s.s.s.IndexSynchronizer] Index rules
2015.09.17 19:03:15 ERROR web[o.a.c.c.C.[.[.[/]] Exception sending context initialized event to listener instance of class org.sonar.server.platform.PlatformServletContextListener
java.lang.IllegalStateException: Could not execute normalization for stack
at org.sonar.server.search.IndexQueue.processActionsIntoQueries(IndexQueue.java:136) ~[sonar-server-5.1.jar:na]
at org.sonar.server.search.IndexQueue.enqueue(IndexQueue.java:82) ~[sonar-server-5.1.jar:na]
at org.sonar.core.persistence.DbSession.commit(DbSession.java:62) ~[sonar-core-5.1.jar:na]
at org.sonar.server.db.BaseDao.synchronizeAfter(BaseDao.java:370) ~[sonar-server-5.1.jar:na]
at org.sonar.server.db.BaseDao.synchronizeAfter(BaseDao.java:356) ~[sonar-server-5.1.jar:na]
at org.sonar.server.search.IndexSynchronizer.synchronize(IndexSynchronizer.java:104) ~[sonar-server-5.1.jar:na]
at org.sonar.server.search.IndexSynchronizer.executeDeprecated(IndexSynchronizer.java:73) ~[sonar-server-5.1.jar:na]
at org.sonar.server.platform.ServerComponents$1.doPrivileged(ServerComponents.java:850) ~[sonar-server-5.1.jar:na]
at org.sonar.server.user.DoPrivileged.execute(DoPrivileged.java:43) ~[sonar-server-5.1.jar:na]
at org.sonar.server.platform.ServerComponents.executeStartupTasks(ServerComponents.java:847) ~[sonar-server-5.1.jar:na]
at org.sonar.server.platform.Platform.executeStartupTasks(Platform.java:126) ~[sonar-server-5.1.jar:na]
at org.sonar.server.platform.Platform.startLevel34Containers(Platform.java:122) ~[sonar-server-5.1.jar:na]
at org.sonar.server.platform.Platform.doStart(Platform.java:81) ~[sonar-server-5.1.jar:na]
at org.sonar.server.platform.PlatformServletContextListener.contextInitialized(PlatformServletContextListener.java:44) ~[sonar-server-5.1.jar:na]
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4720) [tomcat-embed-core-8.0.18.jar:8.0.18]
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5154) [tomcat-embed-core-8.0.18.jar:8.0.18]
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150) [tomcat-embed-core-8.0.18.jar:8.0.18]
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1409) [tomcat-embed-core-8.0.18.jar:8.0.18]
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1399) [tomcat-embed-core-8.0.18.jar:8.0.18]
at java.util.concurrent.FutureTask.run(FutureTask.java:266) [na:1.8.0_60]
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) [na:1.8.0_60]
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) [na:1.8.0_60]
at java.lang.Thread.run(Thread.java:745) [na:1.8.0_60]