You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: url_drop.rb
    path of file: ./repos/jekyll/lib/jekyll/drops
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

module Jekyll
  modul
    
      def categories
        category_set = Set.new
        Array(@obj.data["categories"]).each do |category|
          category_set << category.to_s.downcase
        end
        category_set.to_a.join("/")
      end