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: generator.rb
    path of file: ./repos/vets-api/modules/appeals_api/app/services/appeals_api/pdf_construction
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

require 'central_mail/datestamp_pdf'

module AppealsApi
  module PdfConstruction
    class Generator
      def initialize(appeal, pdf_version: 'v1')
        @appeal = appea
    
      def insert_additional_pages
        # add_additional_pages should always return a Prawn::Document object
        pdf = structure.add_additional_pages

        return @form_fill_path if pdf.blank?

        raise InvalidPdfClass if pdf.class != Prawn::Document

        additional_pages_added_path = "/tmp/#{appeal.id}-additional-pages-tmp.pdf"
        pdf.render_file(additional_pages_added_path) # saves the file

        combine_form_fill_and_additional_pages(additional_pages_added_path)
      end