The website_theme_install needs to reference the module category whose
xml_id is base.module_category_theme_hidden. The problem was that it
needs to do this in a context where the category might not exist (as
auto-created only if a module defines its category as "Theme/Hidden").
To solve the problem, the category was explicitly created by the
website_theme_install module to be able to reference it.
Commit 11812b0b9e removed the "base." part
of the xml_id thinking it was a record which had to be created by the
module. This then wrongly showed the Theme/Hidden modules in the list.
Now the solution came from commit https://github.com/odoo/odoo/commit/c6983137#diff-07193f47475ccdd78f39773a368ce05bL386
which now allows to use the second parameter of ref in a domain
context. This allows to tell the system to not raise an exception if
the ref we want to find does not exist.
qsm-odoo
a00ea2755d