fix case, where settings is False (when run in Plone 4 context)

plone/app/upgrade/v50/betas.py

@@ -14,25 +14,29 @@ def upgrade_markup_controlpanel_settings(context):
     site_properties = portal_properties.site_properties
     # get the new registry
     registry = getUtility(IRegistry)
-
+    # XXX: Somehow this code is excecuted for old migration steps as well
+    # ( < Plone 4 ) and breaks because there is no registry. Looking up the
+    # registry interfaces with 'check=False' will not work, because it will
+    # return a settings object and then fail when we try to access the
+    # attributes.
     try:
         settings = registry.forInterface(
             IMarkupSchema,
             prefix='plone',
         )
     except KeyError:
         settings = False
+    if settings:
+        settings.default_type = site_properties.default_contenttype
 
-    settings.default_type = site_properties.default_contenttype
-
-    forbidden_types = site_properties.getProperty('forbidden_contenttypes')
-    forbidden_types = list(forbidden_types) if forbidden_types else []
+        forbidden_types = site_properties.getProperty('forbidden_contenttypes')
+        forbidden_types = list(forbidden_types) if forbidden_types else []
 
-    portal_transforms = getToolByName(context, 'portal_transforms')
-    allowable_types = portal_transforms.listAvailableTextInputs()
+        portal_transforms = getToolByName(context, 'portal_transforms')
+        allowable_types = portal_transforms.listAvailableTextInputs()
 
-    settings.allowed_types = tuple([
-        _type for _type in allowable_types
-        if _type not in forbidden_types
-        and _type not in 'text/x-plone-outputfilters-html'  # removed, as in plone.app.vocabularies.types  # noqa
-    ])
+        settings.allowed_types = tuple([
+            _type for _type in allowable_types
+            if _type not in forbidden_types
+            and _type not in 'text/x-plone-outputfilters-html'  # removed, as in plone.app.vocabularies.types  # noqa
+        ])