SQL error ORA-01442 when perform confluence upgrade from 5.9.4 to 6.0.5

[xiaobo ding]

I am trying to upgrade confluence which is data center edition from 5.9.4 to 6.0.5. I followed the guide to unzip the installation directory and modify the properties to let the new application point to the old home directory and DB. But when I tried to start the new application, system showed error message about SQL error ORA-01442.

2017-02-21 17:22:28,312 ERROR [localhost-startStop-1] [atlassian.confluence.plugin.PluginFrameworkContextListener] launchUpgrades Upgrade failed, application will not start: Upgrade task com.atlassian.confluence.upgrade.upgradetask.PopulateLowerFieldsUpgradeTask@3f08baa3 failed during the SCHEMA_UPGRADE phase due to: StatementCallback; uncategorized SQLException for SQL [alter table SPACES modify LOWERSPACEKEY nvarchar2(255) not null]; SQL state [72000]; error code [1442]; ORA-01442: column to be modified to NOT NULL is already NOT NULL ; nested exception is java.sql.SQLException: ORA-01442: column to be modified to NOT NULL is already NOT NULL com.atlassian.confluence.upgrade.UpgradeException: Upgrade task com.atlassian.confluence.upgrade.upgradetask.PopulateLowerFieldsUpgradeTask@3f08baa3 failed during the SCHEMA_UPGRADE phase due to: StatementCallback; uncategorized SQLException for SQL [alter table SPACES modify LOWERSPACEKEY nvarchar2(255) not null]; SQL state [72000]; error code [1442]; ORA-01442: column to be modified to NOT NULL is already NOT NULL

I've checked the db table SPACES and found the column LOWERSPACEKEY is not yet NOT NULL. It is very strange why the log said it was already NOT NULL.

Any guys can help?

[xiaobo ding]

After I recovered the system and did the upgrade again, this issue did not appear again.

[WIKI_Queue]

I recovered the system , run the upgrade agian, but still the same issue,

Any suggestion ?