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: config.rb
    path of file: ./repos/nesta/lib/nesta
    
    the code of the file until where you have to start completion: require 'singleton'
require 'yaml'

require_relative './config_file'

module Nesta
  class Config
    include Singleton

    class NotDefined < KeyError; end

    SETTINGS = %w[
      author
      build
      content
      disqus_short_name
      domain
      google_analytics_cod
    
    def fetch(setting, *default)
      setting = setting.to_s
      self.config ||= read_config_file(setting)
      env_config = config.fetch(Nesta::App.environment.to_s, {})
      env_config.fetch(
        setting,
        config.fetch(setting) { raise NotDefined.new(setting) }
      )
    rescue NotDefined
      default.empty? && raise || (return default.first)
    end