fix group and categories page if parent not found

app/controllers/taxonomy_controller.rb

@@ -34,6 +34,7 @@ def nest_categories_children(categories)
     categories.each do |category|
       category[:parentCategory].each do |parent_id|
         parent = category_index[parent_id]
+        next unless parent
         parent[:children] ||= []
         parent[:children] << category
       end