Heroku deployは成功するのですが、App crashedというErrorでアプリを開くことができません

前提・実現したいこと

前提としては、
RailsでRails tutorialを参考にしながら、オリジナルのWEBアプリを作成しています。
ローカルである程度開発が完了したので、Production環境にも反映させようとして、
Herokuにて、BuildとDeployは成功したのですが、
Application Errorが表示され、画面を開くことができないという状況です。

実現したいことは、
Production環境にて、自分が作成したアプリを公開することです。

もし、同じような問題で困った経験のある方や、なにか解決策をご存知の方は、
ご教授いただけますと幸いです。
また、このように質問するのが初めてなので、前提条件が不足しているかもしれません。
その際は、ご指摘いただけますと幸いです。

発生している問題・エラーメッセージ

Heroku logsで出力したログでは以下のようなメッセージが出力されていました。

...

2018-07-21T22:25:53.429050+00:00 app[web.1]: from /app/vendor/bundle/ruby/2.5.0/gems/railties-5.2.0/lib/rails/commands.rb:18:in `<main>'
2018-07-21T22:25:53.429067+00:00 app[web.1]: from /app/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.3.0/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:21:in `require'
2018-07-21T22:25:53.429070+00:00 app[web.1]: from /app/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.3.0/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:21:in `block in require_with_bootsnap_lfi'
2018-07-21T22:25:53.429072+00:00 app[web.1]: from /app/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.3.0/lib/bootsnap/load_path_cache/loaded_features_index.rb:65:in `register'
2018-07-21T22:25:53.429090+00:00 app[web.1]: from /app/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.3.0/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:29:in `require'
2018-07-21T22:25:53.429074+00:00 app[web.1]: from /app/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.3.0/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:20:in `require_with_bootsnap_lfi'
2018-07-21T22:25:53.429092+00:00 app[web.1]: from /app/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/dependencies.rb:283:in `block in require'
2018-07-21T22:25:53.429097+00:00 app[web.1]: from /app/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/dependencies.rb:249:in `load_dependency'
2018-07-21T22:25:53.429099+00:00 app[web.1]: from /app/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/dependencies.rb:283:in `require'
2018-07-21T22:25:53.429102+00:00 app[web.1]: from bin/rails:9:in `<main>'
2018-07-21T22:25:53.436628+00:00 app[web.1]: => Booting Puma
2018-07-21T22:25:53.436633+00:00 app[web.1]: => Rails 5.2.0 application starting in production
2018-07-21T22:25:53.436635+00:00 app[web.1]: => Run `rails server -h` for more startup options
2018-07-21T22:25:53.436636+00:00 app[web.1]: Exiting
2018-07-21T22:25:53.755443+00:00 heroku[web.1]: State changed from starting to crashed
2018-07-22T01:46:55.443194+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/" host=pure-oasis-87548.herokuapp.com request_id=4dd0ea73-12fb-41dc-ba69-e097abcc70b7 fwd="153.214.108.108" dyno= connect= service= status=503 bytes= protocol=https
2018-07-22T01:46:56.415441+00:00 heroku[router]: at=error code=H10 desc="App crashed" method=GET path="/favicon.ico" host=pure-oasis-87548.herokuapp.com request_id=e4cbb4e0-db08-4e97-b4e1-acea10d44d5f fwd="153.214.108.108" dyno= connect= service= status=503 bytes= protocol=https

Heroku run rails cで出力されているエラーメッセージは以下の通りですが、
has_one_attachedメソッドを使用したことはなく、どこを修正すればいいのか検討がついていないという状況です。

...
	 7: from /app/vendor/bundle/ruby/2.5.0/gems/bootsnap-1.3.0/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:21:in `require'
	 6: from /app/vendor/bundle/ruby/2.5.0/gems/activestorage-5.2.0/app/models/active_storage/blob.rb:16:in `<main>'
	 5: from /app/vendor/bundle/ruby/2.5.0/gems/activestorage-5.2.0/app/models/active_storage/blob.rb:23:in `<class:Blob>'
	 4: from /app/vendor/bundle/ruby/2.5.0/gems/activestorage-5.2.0/app/models/active_storage/blob.rb:23:in `include'
	 3: from /app/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/concern.rb:122:in `append_features'
	 2: from /app/vendor/bundle/ruby/2.5.0/gems/activesupport-5.2.0/lib/active_support/concern.rb:122:in `class_eval'
	 1: from /app/vendor/bundle/ruby/2.5.0/gems/activestorage-5.2.0/app/models/active_storage/blob/representable.rb:7:in `block in <module:Representable>'
/app/vendor/bundle/ruby/2.5.0/gems/activerecord-5.2.0/lib/active_record/dynamic_matchers.rb:22:in `method_missing': undefined method `has_one_attached' for #<Class:0x000000000465c3c8> (NoMethodError)

該当のソースコード

Gemfile

source 'https://rubygems.org'
git_source(:github) { |repo| "https://github.com/#{repo}.git" }

ruby '2.5.1'

# Bundle edge Rails instead: gem 'rails', github: 'rails/rails'
gem 'rails', '~> 5.2.0'
# Use sqlite3 as the database for Active Record
#gem 'sqlite3'
# Use Puma as the app server
gem 'puma', '~> 3.11'
# Use SCSS for stylesheets
gem 'sass-rails', '~> 5.0'
# Use Uglifier as compressor for JavaScript assets
gem 'uglifier', '>= 1.3.0'
# See https://github.com/rails/execjs#readme for more supported runtimes
# gem 'mini_racer', platforms: :ruby

# Use CoffeeScript for .coffee assets and views
gem 'coffee-rails', '~> 4.2'
# Turbolinks makes navigating your web application faster. Read more: https://github.com/turbolinks/turbolinks
gem 'turbolinks', '~> 5'
# Build JSON APIs with ease. Read more: https://github.com/rails/jbuilder
gem 'jbuilder', '~> 2.5'
# Use Redis adapter to run Action Cable in production
# gem 'redis', '~> 4.0'
# Use ActiveModel has_secure_password
# gem 'bcrypt', '~> 3.1.7'

gem 'bootstrap-sass', '3.3.7'
gem 'will_paginate',           '3.1.6'
gem 'bootstrap-will_paginate', '1.0.0'

# Use ActiveStorage variant
# gem 'mini_magick', '~> 4.8'

# Use Capistrano for deployment
# gem 'capistrano-rails', group: :development

# Reduces boot times through caching; required in config/boot.rb
gem 'bootsnap', '>= 1.1.0', require: false

group :development, :test do
  # Call 'byebug' anywhere in the code to stop execution and get a debugger console
  gem 'byebug', platforms: [:mri, :mingw, :x64_mingw]
  gem 'sqlite3', '1.3.13'
  gem "simplecov", require: false
end

group :development do
  # Access an interactive console on exception pages or by calling 'console' anywhere in the code.
  gem 'web-console', '>= 3.3.0'
  gem 'listen', '>= 3.0.5', '< 3.2'
  # Spring speeds up development by keeping your application running in the background. Read more: https://github.com/rails/spring
  gem 'spring'
  gem 'spring-watcher-listen', '~> 2.0.0'
end
  group :production do
    gem 'pg', '0.20.0'
  end

group :test do
  # Adds support for Capybara system testing and selenium driver
  gem 'capybara', '>= 2.15', '< 4.0'
  gem 'selenium-webdriver'
  # Easy installation and use of chromedriver to run system tests with Chrome
  gem 'chromedriver-helper'
end

# Windows does not include zoneinfo files, so bundle the tzinfo-data gem
gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]