Upgrade from 5.x to 6.0 java.lang.NullPointerException

Exception thrown during upgrade: null
java.lang.NullPointerException
	at com.atlassian.crowd.embedded.impl.IdentifierUtils.toLowerCase(IdentifierUtils.java:42)
	at com.atlassian.jira.user.ApplicationUserEntity.(ApplicationUserEntity.java:18)
	at com.atlassian.jira.upgrade.tasks.UpgradeTask_Build6040.mapUsername(UpgradeTask_Build6040.java:72)
	at com.atlassian.jira.upgrade.tasks.UpgradeTask_Build6040.doUpgrade(UpgradeTask_Build6040.java:63)
	at com.atlassian.jira.upgrade.UpgradeManagerImpl.doUpgradeTaskSuccess(UpgradeManagerImpl.java:673)
	at com.atlassian.jira.upgrade.UpgradeManagerImpl.runUpgradeTasks(UpgradeManagerImpl.java:526)
	at com.atlassian.jira.upgrade.UpgradeManagerImpl.doUpgrade(UpgradeManagerImpl.java:456)
	at com.atlassian.jira.upgrade.UpgradeManagerImpl.doUpgradeIfNeeded(UpgradeManagerImpl.java:399)
	at com.atlassian.jira.upgrade.UpgradeManagerImpl.doUpgradeIfNeededAndAllowed(UpgradeManagerImpl.java:333)
	at com.atlassian.jira.upgrade.UpgradeLauncher.checkIfUpgradeNeeded(UpgradeLauncher.java:100)
	at com.atlassian.jira.upgrade.UpgradeLauncher.start(UpgradeLauncher.java:49)
	at com.atlassian.jira.startup.DefaultJiraLauncher$3.run(DefaultJiraLauncher.java:117)
	at com.atlassian.jira.config.database.DatabaseConfigurationManagerImpl.doNowOrEnqueue(DatabaseConfigurationManagerImpl.java:315)
	at com.atlassian.jira.config.database.DatabaseConfigurationManagerImpl.doNowOrWhenDatabaseActivated(DatabaseConfigurationManagerImpl.java:209)
	at com.atlassian.jira.startup.DefaultJiraLauncher.postDbLaunch(DefaultJiraLauncher.java:105)
	at com.atlassian.jira.startup.DefaultJiraLauncher.access$100(DefaultJiraLauncher.java:30)
	at com.atlassian.jira.startup.DefaultJiraLauncher$1.run(DefaultJiraLauncher.java:69)
	at com.atlassian.jira.util.devspeed.JiraDevSpeedTimer.run(JiraDevSpeedTimer.java:33)
	at com.atlassian.jira.startup.DefaultJiraLauncher.start(DefaultJiraLauncher.java:64)
	at com.atlassian.jira.startup.LauncherContextListener.contextInitialized(LauncherContextListener.java:54)
	at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4791)
	at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5285)
	at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
	at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1559)
	at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1549)
	at java.util.concurrent.FutureTask$Sync.innerRun(Unknown Source)
	at java.util.concurrent.FutureTask.run(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
	at java.lang.Thread.run(Unknown Source)