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: pipeline.rb
    path of file: ./repos/gitlabhq/lib/bulk_imports
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

module BulkImports
  module Pipeline
    extend ActiveSupport::Concern
    include Gitlab::Utils::StrongMemoize
    include Gitlab::ClassAttributes
    include Runner

    NotAllowedError = Class.new(Stan
    
      def transformers
        strong_memoize(:transformers) do
          defined_transformers = self.class.transformers.map(&method(:instantiate))

          transformers = []
          transformers << self if respond_to?(:transform)
          transformers.concat(defined_transformers)
          transformers
        end
      end