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: notify.rb
    path of file: ./repos/gitlabhq/app/mailers
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

class Notify < ApplicationMailer
  include ActionDispatch::Routing::PolymorphicRoutes
  include GitlabRoutingHelper
  include EmailsHelper
  include ReminderEmailsHelper
  include IssuablesHelper

  include Emails::Shared
  include Emails::Issues
  include Emails::MergeRequests
  include Emails::Notes
  include Emails::PagesDo
    
  def mail_answer_note_thread(model, note, headers = {})
    headers['Message-ID'] = message_id(note)
    headers['In-Reply-To'] = message_id(note.references.last)
    headers['References'] = note.references.map { |ref| message_id(ref) }

    headers['X-GitLab-Discussion-ID'] = note.discussion.id if note.part_of_discussion? || note.can_be_discussion_note?

    headers[:subject] = "Re: #{headers[:subject]}" if headers[:subject]

    mail_thread(model, headers)
  end