Herokuでrailsアプリのデプロイでエラー

rails初心者です。
rails tutorialでtutorialに沿ってherokuでデプロイしようとしたら、
Precompiling assets failed.
という結果が出てしまい、色々調べたものの解決せず、困っています。
お知恵をお借りできれば幸いです。

cloud9でrailsは6.0.3、tutorialは6版にそって、コピペしただけです。

発生している問題・エラーメッセージ

Counting objects: 120, done.
Compressing objects: 100% (103/103), done.
Writing objects: 100% (120/120), 27.76 KiB | 1.21 MiB/s, done.
Total 120 (delta 18), reused 0 (delta 0)
remote: Compressing source files... done.
remote: Building source:
remote:
remote: ! Warning: Multiple default buildpacks reported the ability to handle this app. The first buildpack in the list below will be used.
remote: Detected buildpacks: Ruby,Node.js
remote: See https://devcenter.heroku.com/articles/buildpacks#buildpack-detect-order
remote: -----> Ruby app detected
remote: -----> Installing bundler 1.17.3
remote: -----> Removing BUNDLED WITH version in the Gemfile.lock
remote: -----> Compiling Ruby/Rails
remote: -----> Using Ruby version: ruby-2.6.6
remote: -----> Installing dependencies using bundler 1.17.3
remote: Running: bundle install --without development:test --path vendor/bundle --binstubs vendor/bundle/bin -j4 --deployment
remote: 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.

省略

remote: info No lockfile found.
remote: [1/4] Resolving packages...
remote: [2/4] Fetching packages...
remote: [3/4] Linking dependencies...
remote: [4/4] Building fresh packages...
remote: Done in 0.63s.
remote: I, [2020-09-08T16:05:52.100272 #1297] INFO -- : Writing /tmp/build_7379a3bb/public/assets/application-e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855.css
remote: I, [2020-09-08T16:05:52.100961 #1297] INFO -- : Writing /tmp/build_7379a3bb/public/assets/application-e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855.css.gz
remote: webpack binstubs not found.
remote: Have you run rails webpacker:install ?
remote: Make sure the bin directory or binstubs are not included in .gitignore
remote: Exiting!
remote:
remote: !
remote: ! Precompiling assets failed.
remote: !
remote: ! Push rejected, failed to compile Ruby app.
remote:
remote: ! Push failed
remote: Verifying deploy...
remote:
remote: ! Push rejected to desolate-sierra-59533.
remote:
To https://git.heroku.com/desolate-sierra-59533.git
! [remote rejected] master -> master (pre-receive hook declined)
error: failed to push some refs to 'https://git.heroku.com/desolate-sierra-59533.git'

該当のソースコード

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

gem 'rails', '6.0.3'
gem 'puma', '4.3.4'
gem 'sass-rails', '5.1.0'
gem 'webpacker', '4.0.7'
gem 'turbolinks', '5.2.0'
gem 'jbuilder', '2.9.1'
gem 'bootsnap', '1.4.5', require: false

group :development, :test do
gem 'sqlite3', '1.4.1'
gem 'byebug', '11.0.1', platforms: [:mri, :mingw, :x64_mingw]
end

group :development do
gem 'web-console', '4.0.1'
gem 'listen', '3.1.5'
gem 'spring', '2.1.0'
gem 'spring-watcher-listen', '2.0.1'
end

group :test do
gem 'capybara', '3.28.0'
gem 'selenium-webdriver', '3.142.4'
gem 'webdrivers', '4.1.2'
gem 'rails-controller-testing', '1.0.4'
gem 'minitest', '5.11.3'
gem 'minitest-reporters', '1.3.8'
gem 'guard', '2.16.2'
gem 'guard-minitest', '2.4.6'
end

group :production do
gem 'pg', '1.1.4'
end

Windows ではタイムゾーン情報用の tzinfo-data gem を含める必要があります

gem 'tzinfo-data', platforms: [:mingw, :mswin, :x64_mingw, :jruby]

試したこと

config.assets.initialize_on_precompile = false
をappcation.rbに追記しましたが、同様のエラーが発生しました。
bundle updateやcommitをし直しましたが、いずれも同じ結果でした。

hatsu

2020/09/08 16:36

herokuでRAILS_MASTER_KEYという環境変数は持っているでしょうか？ heroku config:get RAILS_MASTER_KEY などで確認ができます。設定されていなけれ、heroku config:set RAILS_MASTER_KEY="値を入力" でセットできます。こちらがCLIコマンドの参考です。https://devcenter.heroku.com/articles/config-vars#using-the-heroku-cli