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: estimator.rb
    path of file: ./repos/openfoodnetwork/engines/order_management/app/services/order_management/subscriptions
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

require 'open_food_network/scope_variant_to_hub'

# R
    
      def fee_calculator
        return @fee_calculator unless @fee_calculator.nil?

        next_oc = subscription.schedule&.current_or_next_order_cycle
        return nil unless shop && next_oc

        @fee_calculator = OpenFoodNetwork::EnterpriseFeeCalculator.new(shop, next_oc)
      end