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: random_uniq_attr.rb
    path of file: ./repos/rails_stuff/lib/rails_stuff
    
    the code of the file until where you have to start completion: module RailsStuff
  # Provides save way to generate uniq random values for ActiveRecord models.
  # You need to make field nullable
    
    def random_uniq_attr(field, **options, &block)
      set_method = :"set_#{field}"
      generate_method = :"generate_#{field}"
      max_attempts = options.fetch(:max_attempts) { MAX_ATTEMPTS }

      after_create set_method, unless: :"#{field}?"

      # def self.generate_key
      define_singleton_method generate_method, &(block || DEFAULT_GENERATOR)

      # def set_key
      define_method(set_method) do
        attempt = 0
        begin
          raise 'Available only for persisted record' unless persisted?
          transaction(requires_new: true) do
            new_value = self.class.send(generate_method, self)
            update_column field, new_value # rubocop:disable Rails/SkipsModelValidations
          end
        rescue ActiveRecord::RecordNotUnique
          attempt += 1
          raise if attempt > max_attempts
          retry
        end
      end