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: personalization.rb
    path of file: ./repos/sendgrid-ruby/lib/sendgrid/helpers/mail
    
    the code of the file until where you have to start completion: require 'json'

module SendGrid
  class Personalization
    attr_reader :tos, :from, :ccs, :bccs, :headers, :substitutions, :cu
    
    def duplicate?(addition)
      additional_email = addition.email.downcase

      [@tos, @ccs, @bccs].flatten.each do |elm|
        return true if elm&.dig('email')&.downcase == additional_email
      end

      false
    end