Ruby on Rails チュートリアル13章　herokuデプロイ時に環境変数が無いと起きるエラー

前提・実現したいこと

現在、Rails tutorial　13章の最後で躓いています。

テストは全て通っており、ローカル環境だと画像投稿も成功しています。

しかし、herokuでデプロイする時に下記のエラーが発生します。

発生している問題・エラーメッセージ

AccessキーとSecretキーが渡されていないとエラーメッセージが出されます。

-----> Ruby app detected
-----> Compiling Ruby/Rails
-----> Using Ruby version: ruby-2.6.0
-----> Installing dependencies using bundler 1.15.2
       Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin -j4 --deployment
       Warning: the running version of Bundler (1.17.2) is older than the version that created the lockfile (1.17.3). We suggest you upgrade to the latest version of Bundler by running `gem install bundler`.
       The dependency tzinfo-data (>= 0) will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for x86-mingw32, x86-mswin32, x64-mingw32, java. To add those platforms to the bundle, run `bundle lock --add-platform x86-mingw32 x86-mswin32 x64-mingw32 java`.
       Fetching gem metadata from https://rubygems.org/.........
       Using rake 12.3.2
(略)
       Post-install message from fog:
       ------------------------------
       Thank you for installing fog!
       
       IMPORTANT NOTICE:
       If there's a metagem available for your cloud provider, e.g. `fog-aws`,
       you should be using it instead of requiring the full fog collection to avoid
       unnecessary dependencies.
       
       'fog' should be required explicitly only if:
       - The provider you use doesn't yet have a metagem available.
       - You require Ruby 1.9.3 support.
       ------------------------------
       Removing bundler (1.15.2)
       Removing autoprefixer-rails (9.5.0)
       Removing sass (3.7.3)
       Removing minitest (5.10.3)
       Removing rack (2.0.6)
       Bundle completed (39.90s)
       Cleaning up the bundler cache.
       Warning: the running version of Bundler (1.17.2) is older than the version that created the lockfile (1.17.3). We suggest you upgrade to the latest version of Bundler by running `gem install bundler`.
       The dependency tzinfo-data (>= 0) will be unused by any of the platforms Bundler is installing for. Bundler is installing for ruby but the dependency is only for x86-mingw32, x86-mswin32, x64-mingw32, java. To add those platforms to the bundle, run `bundle lock --add-platform x86-mingw32 x86-mswin32 x64-mingw32 java`.
-----> Installing node-v10.14.1-linux-x64
-----> Detecting rake tasks
-----> Preparing app for Rails asset pipeline
       Running: rake assets:precompile
       rake aborted!
       ArgumentError: Missing required arguments: aws_access_key_id, aws_secret_access_key
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/fog-core-1.45.0/lib/fog/core/service.rb:244:in `validate_options'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/fog-core-1.45.0/lib/fog/core/service.rb:268:in `handle_settings'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/fog-core-1.45.0/lib/fog/core/service.rb:98:in `new'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/fog-core-1.45.0/lib/fog/core/services_mixin.rb:16:in `new'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/fog-core-1.45.0/lib/fog/storage.rb:27:in `new'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/carrierwave-1.2.2/lib/carrierwave/uploader/configuration.rb:124:in `eager_load_fog'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/carrierwave-1.2.2/lib/carrierwave/uploader/configuration.rb:137:in `fog_credentials='
       /tmp/build_33683b461f648aad077409566a3b7c1f/config/initializers/carrier_wave.rb:3:in `block in <top (required)>'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/carrierwave-1.2.2/lib/carrierwave/uploader/configuration.rb:159:in `configure'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/carrierwave-1.2.2/lib/carrierwave.rb:14:in `configure'
       /tmp/build_33683b461f648aad077409566a3b7c1f/config/initializers/carrier_wave.rb:2:in `<top (required)>'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/activesupport-5.1.6/lib/active_support/dependencies.rb:286:in `load'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/activesupport-5.1.6/lib/active_support/dependencies.rb:286:in `block in load'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/activesupport-5.1.6/lib/active_support/dependencies.rb:258:in `load_dependency'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/activesupport-5.1.6/lib/active_support/dependencies.rb:286:in `load'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/railties-5.1.6/lib/rails/engine.rb:655:in `block in load_config_initializer'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/activesupport-5.1.6/lib/active_support/notifications.rb:168:in `instrument'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/railties-5.1.6/lib/rails/engine.rb:654:in `load_config_initializer'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/railties-5.1.6/lib/rails/engine.rb:612:in `block (2 levels) in <class:Engine>'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/railties-5.1.6/lib/rails/engine.rb:611:in `each'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/railties-5.1.6/lib/rails/engine.rb:611:in `block in <class:Engine>'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/railties-5.1.6/lib/rails/initializable.rb:30:in `instance_exec'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/railties-5.1.6/lib/rails/initializable.rb:30:in `run'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/railties-5.1.6/lib/rails/initializable.rb:59:in `block in run_initializers'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/railties-5.1.6/lib/rails/initializable.rb:48:in `each'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/railties-5.1.6/lib/rails/initializable.rb:48:in `tsort_each_child'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/railties-5.1.6/lib/rails/initializable.rb:58:in `run_initializers'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/railties-5.1.6/lib/rails/application.rb:353:in `initialize!'
       /tmp/build_33683b461f648aad077409566a3b7c1f/config/environment.rb:5:in `<top (required)>'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/railties-5.1.6/lib/rails/application.rb:329:in `require'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/railties-5.1.6/lib/rails/application.rb:329:in `require_environment!'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/railties-5.1.6/lib/rails/application.rb:445:in `block in run_tasks_blocks'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/sprockets-rails-3.2.1/lib/sprockets/rails/task.rb:62:in `block (2 levels) in define'
       /tmp/build_33683b461f648aad077409566a3b7c1f/vendor/bundle/ruby/2.6.0/gems/rake-12.3.2/exe/rake:27:in `<top (required)>'
       Tasks: TOP => environment
       (See full trace by running task with --trace)
 !
 !     Precompiling assets failed.
 !
 !     Push rejected, failed to compile Ruby app.
 !     Push failed

該当のソースコード

gemfile
1
2group :production do
3  gem 'pg',   '0.20.0'
4  gem 'fog-aws'
5end
6
7# Windows環境ではtzinfo-dataというgemを含める必要があります
8gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

if Rails.env.production?
  CarrierWave.configure do |config|
    config.fog_provider = 'fog/aws'
    config.fog_credentials = {
      # Amazon S3用の設定
      :provider              => 'AWS',
      :region                => ENV['S3_REGION'],     # 例: 'ap-northeast-1'
      :aws_access_key_id     => ENV['S3_ACCESS_KEY'],
      :aws_secret_access_key => ENV['S3_SECRET_KEY']
    }
    config.fog_directory     =  ENV['S3_BUCKET']
  end
end

class PictureUploader < CarrierWave::Uploader::Base
  include CarrierWave::MiniMagick
  process resize_to_limit: [400, 400]

  if Rails.env.production?
    storage :fog
  else
    storage :file
  end

  # アップロードファイルの保存先ディレクトリは上書き可能
  # 下記はデフォルトの保存先  
  def store_dir
    "uploads/#{model.class.to_s.underscore}/#{mounted_as}/#{model.id}"
  end

  # アップロード可能な拡張子のリスト
  def extension_whitelist
    %w(jpg jpeg gif png)
  end
end