Sample plugin text - not working

plugin.rb

# name: replyto-individual plugin
# about: A plugin that allows exposure of the sender's email address for functionality
#        similar to GNU/Mailman's Reply_Goes_To_List = Poster
# version: 0.0.1
# authors: Tarek Loubani <tarek@tarek.org>
# license: aGPLv3

PLUGIN_NAME ||= "replyto-individual".freeze

require 'email/message_builder.rb'

Email::MessageBuilder.class_eval do
  def header_args
  byebug
    result = {}
    if @opts[:add_unsubscribe_link]
      result['List-Unsubscribe'] = "<#{template_args[:user_preferences_url]}>"
    end

    if @opts[:mark_as_reply_to_auto_generated]
      result[REPLY_TO_AUTO_GENERATED_HEADER_KEY] = REPLY_TO_AUTO_GENERATED_HEADER_VALUE
    end

    result['X-Discourse-Post-Id'] = @opts[:post_id].to_s if @opts[:post_id]
    result['X-Discourse-Topic-Id'] = @opts[:topic_id].to_s if @opts[:topic_id]

    if allow_reply_by_email?
      result['X-Discourse-Reply-Key'] = reply_key
      if @opts[:private_reply] == true
        result['Reply-To'] = reply_by_email_address
      else
        p = Post.find_by_id @opts[:post_id]
        result['Reply-To'] = "#{p.user.name} <#{p.user.email}>"
        result['CC'] = reply_by_email_address
      end
    else
      result['Reply-To'] = from_value
    end

    result.merge(MessageBuilder.custom_headers(SiteSetting.email_custom_headers))
  end
end