• The intention of Fix NamespaceVersioning ignoring DEFAULT_VERSION on non-None namespaces #7278 seems to be to deal with situations where DEFAULT_VERSION is ignored. The description of the fix relates to non-None values of DEFAULT_VERSION.
• When DEFAULT_VERSION is None and ALLOWED_VERSIONS is non-empty, the new code now raises 404.
• In 3.14, None would be returned in this case. This suddenly raises 404 where previously the view was properly run.

This is a regression that significantly changes the API. The change should be reverted.