better add some tests here tomorrow

app/controllers/categories_controller.rb

@@ -7,7 +7,7 @@ class CategoriesController < ApplicationController
   skip_before_filter :check_xhr, only: [:index]
 
   def index
-    @list = CategoryList.new(current_user)
+    @list = CategoryList.new(guardian)
     discourse_expires_in 1.minute
     respond_to do |format|
       format.html { render }

app/models/category_list.rb

@@ -4,6 +4,8 @@ class CategoryList
   attr_accessor :categories, :topic_users, :uncategorized
 
   def initialize(guardian)
+    guardian ||= Guardian.new
+
     @categories = Category
                     .includes(featured_topics: [:category])
                     .includes(:featured_users)