Log:
2014-09-16 15:02:27,373 localhost-startStop-1 INFO [atlassian.jira.upgrade.UpgradeManagerImpl] Performing Upgrade Task: JRA-34394: Fixing incorrect watch count for cloned issues
2014-09-16 15:02:27,396 localhost-startStop-1 ERROR [atlassian.jira.upgrade.UpgradeManagerImpl] Exception thrown during upgrade: null
java.lang.NullPointerException
at com.atlassian.jira.upgrade.tasks.UpgradeTask_Build6331$2.result(UpgradeTask_Build6331.java:122)
at com.atlassian.jira.upgrade.tasks.UpgradeTask_Build6331$2.result(UpgradeTask_Build6331.java:98)
at com.atlassian.jira.entity.SelectQueryImpl$ExecutionContextImpl.consumeWith(SelectQueryImpl.java:247)
at com.atlassian.jira.upgrade.tasks.UpgradeTask_Build6331.findBrokenIssues(UpgradeTask_Build6331.java:95)
at com.atlassian.jira.upgrade.tasks.UpgradeTask_Build6331.doUpgrade(UpgradeTask_Build6331.java:65)
at com.atlassian.jira.upgrade.UpgradeManagerImpl.doUpgradeTaskSuccess(UpgradeManagerImpl.java:693)
at com.atlassian.jira.upgrade.UpgradeManagerImpl.runUpgradeTasks(UpgradeManagerImpl.java:542)
at com.atlassian.jira.upgrade.UpgradeManagerImpl.doUpgrade(UpgradeManagerImpl.java:471)
at com.atlassian.jira.upgrade.UpgradeManagerImpl.doUpgradeIfNeeded(UpgradeManagerImpl.java:413)
at com.atlassian.jira.upgrade.UpgradeManagerImpl.doUpgradeIfNeededAndAllowed(UpgradeManagerImpl.java:348)
at com.atlassian.jira.upgrade.UpgradeLauncher.checkIfUpgradeNeeded(UpgradeLauncher.java:106)
at com.atlassian.jira.upgrade.UpgradeLauncher.start(UpgradeLauncher.java:54)
at com.atlassian.jira.startup.ActiveServicesLauncher.start(ActiveServicesLauncher.java:42)
at com.atlassian.jira.startup.DefaultJiraLauncher$3.run(DefaultJiraLauncher.java:136)
at com.atlassian.jira.config.database.DatabaseConfigurationManagerImpl.doNowOrEnqueue(DatabaseConfigurationManagerImpl.java:324)
at com.atlassian.jira.config.database.DatabaseConfigurationManagerImpl.doNowOrWhenDatabaseActivated(DatabaseConfigurationManagerImpl.java:214)
at com.atlassian.jira.startup.DefaultJiraLauncher.postDbLaunch(DefaultJiraLauncher.java:118)
at com.atlassian.jira.startup.DefaultJiraLauncher.access$100(DefaultJiraLauncher.java:32)
at com.atlassian.jira.startup.DefaultJiraLauncher$1.run(DefaultJiraLauncher.java:81)
at com.atlassian.jira.util.devspeed.JiraDevSpeedTimer.run(JiraDevSpeedTimer.java:34)
at com.atlassian.jira.startup.DefaultJiraLauncher.start(DefaultJiraLauncher.java:76)
at com.atlassian.jira.startup.LauncherContextListener.contextInitialized(LauncherContextListener.java:71)
at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4992)
at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5490)
at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1575)
at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1565)
at java.util.concurrent.FutureTask$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)

Workaround:
update jiraissue set WATCHES = 0 where WATCHES is null