Unable to create spaces in 6.11.x to 6.15.2 when a space blueprint plugin has been removed

Summary

A bug in 6.11.0 to 6.15.2 leads to the Create Space dialog not loading, and giving an "unknown server error" in the UI after clicking on the Create Space button.

A pre-exiting KB has almost 100% effectiveness with some exceptions that are environmental, not the application. Here's the KB:

• https://confluence.atlassian.com/confkb/creating-new-page-or-space-loads-forever-744329880.html

This was caused by the space blueprints table AO_54C900_SPACE_BLUEPRINT_AO containing a reference to a blueprint that was no longer available.
E.g. the plugin that included the blueprint has been uninstalled.

Another situation is where the blueprint was partially enabled.

This bug is fixed in 6.13.5 and 6.15.3.

Logs

This is the logging by default that is used to identify the problem:

2019-01-23 15:19:28,291 WARN [http-nio-8090-exec-4] [confluence.impl.hibernate.ConfluenceHibernateTransactionManager] doRollback Performing rollback. Transactions:
  ->[PluginReadWriteTx]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT (Session #1723296075)
 -- referer: https://mywiki.com/admin/viewlog4j.action | url: /rest/create-dialog/1.0/space-blueprint/dialog/web-items | traceId: 6b739b69b3cbee0b | userName: supertest@test.com

Logs with debug on for AO:

2019-01-23 15:19:28,266 DEBUG [http-nio-8090-exec-4] [net.java.ao.sql] onSql SELECT "NAME","PROMOTED_BPS","PLUGIN_CLONE","CATEGORY","ID","UUID","PLUGIN_MODULE_KEY" FROM "AO_54C900_SPACE_BLUEPRINT_AO"
2019-01-23 15:19:28,268 DEBUG [http-nio-8090-exec-2] [net.java.ao.sql] onSql SELECT "ID","CONTENT" FROM "AO_21F425_MESSAGE_AO" LIMIT 1
2019-01-23 15:19:28,274 DEBUG [http-nio-8090-exec-4] [net.java.ao.sql] onSql SELECT "HOME_PAGE_ID" FROM "AO_54C900_SPACE_BLUEPRINT_AO" WHERE "ID" = ?
2019-01-23 15:19:28,276 DEBUG [http-nio-8090-exec-2] [net.java.ao.sql] onSql SELECT "ID","CONTENT" FROM "AO_21F425_MESSAGE_AO" LIMIT 1
2019-01-23 15:19:28,277 DEBUG [http-nio-8090-exec-4] [net.java.ao.sql] onSql SELECT "HOME_PAGE_ID" FROM "AO_54C900_SPACE_BLUEPRINT_AO" WHERE "ID" = ?
2019-01-23 15:19:28,281 DEBUG [http-nio-8090-exec-4] [net.java.ao.sql] onSql SELECT "HOME_PAGE_ID" FROM "AO_54C900_SPACE_BLUEPRINT_AO" WHERE "ID" = ?
2019-01-23 15:19:28,286 DEBUG [http-nio-8090-exec-4] [net.java.ao.sql] onSql SELECT "UUID" FROM "AO_54C900_C_TEMPLATE_REF" WHERE "ID" = ?
2019-01-23 15:19:28,291 WARN [http-nio-8090-exec-4] [confluence.impl.hibernate.ConfluenceHibernateTransactionManager] doRollback Performing rollback. Transactions:
  ->[PluginReadWriteTx]: PROPAGATION_REQUIRED,ISOLATION_DEFAULT (Session #1723296075)
 -- referer: https://mywiki.com/admin/viewlog4j.action | url: /rest/create-dialog/1.0/space-blueprint/dialog/web-items | traceId: 6b739b69b3cbee0b | userName: supertest@test.com

It happens on UPGRADES from 6.x to 6.11.x or later versions and it happens with all databases, no common plugin used, dropping/truncating the tables always resolve the problem, with just one exception.

Steps to reproduce

There are a few ways to reproduce it.  The most common and dangerous is:

• Create a space using the a space blueprint
• Disable the plugin module that provides that space blueprint
• Upgrade to 6.11.x or above
• Try to create a space

The "it happens on upgrade" is because the bug was introduced there, and in previous versions it was fine to disable the space blueprint of a plugin module.

• When using 6.11.x or above
• Create a space using the a space blueprint
• Disable the plugin module that provides that space blueprint
• Try to create a space

Another way is to just disable a space blueprint plugin module without disabling the space blueprint item module, e.g.

• When using 6.11.x or above
• Go to Manage apps
• Turn off the team-space-blueprint module
• Try to create a space

Workarounds

• Upgrade to 6.15.3 or 6.13.5
• Create spaces using the old UI. You don't get to choose a space type, but you can still create spaces. Start at http://<baseurl>/<contextpath>/spaces/createspace-start.action
• If you have disabled or uninstalled any space blueprint plugins or plugin modules you used to use, then re-enable them
• If those aren't enough, follow this KB to delete old space blueprint use from the database https://confluence.atlassian.com/confkb/creating-new-page-or-space-loads-forever-744329880.html