recognize instances where group visibility levels are unavailable

app/helpers/visibility_level_helper.rb

@@ -96,6 +96,7 @@ module VisibilityLevelHelper
             to: :current_application_settings
 
   def skip_level?(form_model, level)
-    form_model.is_a?(Project) && !form_model.visibility_level_allowed?(level)
+    return false unless form_model.respond_to?(:visibility_level_allowed?)
+    !form_model.visibility_level_allowed?(level)
   end
 end

app/models/group.rb

@@ -136,6 +136,12 @@ class Group < Namespace
     children.where('visibility_level > ?', level).none?
   end
 
+  def visibility_level_allowed?(level = self.visibility_level)
+    visibility_level_allowed_by_parent?(level) &&
+      visibility_level_allowed_by_projects?(level) &&
+      visibility_level_allowed_by_sub_groups?(level)
+  end
+
   def avatar_url(**args)
     # We use avatar_path instead of overriding avatar_url because of carrierwave.
     # See https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/11001/diffs#note_28659864