Upgrading 4.0.10 to Plone 5 (missing IRegistry?) - plone

Question

I'm trying to upgrade a Plone 4.0.10 site to 5.0. I went through the upgrade to 4.3.6 and somewhat painfully got it to work there. In my Data.fs I have two Plone sites: the site in question, and another one that has nothing but the default content (News, Events, Users). When I moved the Data.fs and blobs from the 4.3.6 to the Plone 5 instance, the "empty" site upgraded fine. However, if I even try to go to the ZMI root for the production site, or to load the site, I get this:
2015-12-05 17:19:24 ERROR Zope.SiteErrorLog 1449364764.10.146181213601 http://localhost:8080/mysite
Traceback (innermost last):
Module ZPublisher.Publish, line 127, in publish
Module ZPublisher.BaseRequest, line 444, in traverse
Module ZPublisher.BeforeTraverse, line 97, in __call__
Module Products.CMFCore.PortalObject, line 75, in __before_publishing_traverse__
Module zope.event, line 31, in notify
Module zope.component.event, line 24, in dispatch
Module zope.component._api, line 136, in subscribers
Module zope.component.registry, line 321, in subscribers
Module zope.interface.adapter, line 585, in subscribers
Module zope.component.event, line 32, in objectEventNotify
Module zope.component._api, line 136, in subscribers
Module zope.component.registry, line 321, in subscribers
Module zope.interface.adapter, line 585, in subscribers
Module plone.app.theming.plugins.hooks, line 33, in onRequest
Module plone.app.theming.policy, line 91, in isThemeEnabled
AttributeError: 'NoneType' object has no attribute 'enabled'
I don't know why plone.app.theming is involved, since the old site had no Diazo theme, and I'm just loading the ZMI. Also, the problem seems to be that there is no IRegistry:
In plone.app.theming.policy.getSettings:
def getSettings(self):
"""Settings for current theme."""
registry = queryUtility(IRegistry)
And registry at this point is None, and so is settings in plone.app.theming.policy.isThemeEnabled.
Any suggestions on how to proceed?

Answer 1

plone.app.theming has to be installed in Plone 4. Include p.a.t in your Plone 4.3.6 Site and re-upgrade.
(How to upgrade sites to Plone 5, 24:15)