いつも大変お世話になっております。

今回、初めてRailsアプリを作成し、VPSにデプロイしようとしているところです。

(初心者向け）vpsを契約して、capistrano3でRailsアプリをデプロイするまで [その1 サーバー設定編]
(初心者向け）vpsを契約して、Capistrano3でRailsアプリをデプロイするまで [その2 ローカル設定編]

手順は上記ページを参考にさせてもらっています。
現在はその2の「4-2 デプロイの実行」を行っているところなんですが、どうしても解決できないエラーが発生していて困っています。

まず、ターミナルでbundle exec cap production deploy --traceを実行したときに表示されるエラーは以下になります。
あまりにも長いので関係ありそうなところだけ掲載します。

/Users/user/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/sshkit-1.20.0/lib/sshkit/command.rb:97:in `exit_status=': bundle exit status: 1 (SSHKit::Command::Failed)
bundle stdout: Nothing written
bundle stderr: master failed to start, check stderr log for details
        1: from /Users/user/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/sshkit-1.20.0/lib/sshkit/runners/parallel.rb:11:in `block (2 levels) in execute'
/Users/user/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/sshkit-1.20.0/lib/sshkit/runners/parallel.rb:15:in `rescue in block (2 levels) in execute': Exception while executing as user@150.95.152.189: bundle exit status: 1 (SSHKit::Runner::ExecuteError)
bundle stdout: Nothing written
bundle stderr: master failed to start, check stderr log for details
cap aborted!
SSHKit::Runner::ExecuteError: Exception while executing as user@150.95.152.189: bundle exit status: 1
bundle stdout: Nothing written
bundle stderr: master failed to start, check stderr log for details
/Users/user/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/sshkit-1.20.0/lib/sshkit/runners/parallel.rb:15:in `rescue in block (2 levels) in execute'
/Users/user/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/sshkit-1.20.0/lib/sshkit/runners/parallel.rb:11:in `block (2 levels) in execute'

Caused by:
SSHKit::Command::Failed: bundle exit status: 1
bundle stdout: Nothing written
bundle stderr: master failed to start, check stderr log for details
/Users/user/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/sshkit-1.20.0/lib/sshkit/command.rb:97:in `exit_status='
/Users/user/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/sshkit-1.20.0/lib/sshkit/backends/netssh.rb:170:in `execute_command'
/Users/user/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/sshkit-1.20.0/lib/sshkit/backends/abstract.rb:148:in `block in create_command_and_execute'
/Users/user/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/sshkit-1.20.0/lib/sshkit/backends/abstract.rb:148:in `tap'
/Users/user/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/sshkit-1.20.0/lib/sshkit/backends/abstract.rb:148:in `create_command_and_execute'
/Users/user/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/sshkit-1.20.0/lib/sshkit/backends/abstract.rb:80:in `execute'
/Users/user/Products/blog/lib/capistrano/tasks/unicorn.rb:11:in `block in start_unicorn'
/Users/user/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/sshkit-1.20.0/lib/sshkit/backends/abstract.rb:92:in `within'
/Users/user/Products/blog/lib/capistrano/tasks/unicorn.rb:10:in `start_unicorn'
/Users/user/Products/blog/lib/capistrano/tasks/unicorn.rb:53:in `block (3 levels) in <top (required)>'
/Users/user/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/sshkit-1.20.0/lib/sshkit/backends/abstract.rb:31:in `instance_exec'
/Users/user/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/sshkit-1.20.0/lib/sshkit/backends/abstract.rb:31:in `run'
/Users/user/.rbenv/versions/2.6.3/lib/ruby/gems/2.6.0/gems/sshkit-1.20.0/lib/sshkit/runners/parallel.rb:12:in `block (2 levels) in execute'
Tasks: TOP => unicorn:restart
The deploy has failed with an error: Exception while executing as user@150.95.152.189: bundle exit status: 1
bundle stdout: Nothing written
bundle stderr: master failed to start, check stderr log for details
** Invoke deploy:failed (first_time)
** Execute deploy:failed

続いて、VPSのunicorn.logのエラー内容が以下になります。

[fog][DEPRECATION] Fog::Storage::AWS is deprecated, please use Fog::AWS::Storage.
[fog][WARNING] Unrecognized arguments: region, aws_access_key_id, aws_secret_access_key
bundler: failed to load command: unicorn (/var/www/app/shared/bundle/ruby/2.6.0/bin/unicorn)
TypeError: no implicit conversion of nil into String
  /var/www/app/shared/bundle/ruby/2.6.0/gems/fog-aws-3.5.2/lib/fog/aws/signaturev4.rb:12:in `+'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/fog-aws-3.5.2/lib/fog/aws/signaturev4.rb:12:in `initialize'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/fog-aws-3.5.2/lib/fog/aws/storage.rb:544:in `new'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/fog-aws-3.5.2/lib/fog/aws/storage.rb:544:in `setup_credentials'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/fog-aws-3.5.2/lib/fog/aws/storage.rb:527:in `initialize'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/fog-core-2.1.0/lib/fog/core/service.rb:115:in `new'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/fog-core-2.1.0/lib/fog/core/service.rb:115:in `new'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/fog-aws-3.5.2/lib/fog/aws/storage.rb:788:in `new'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/fog-core-2.1.0/lib/fog/core/services_mixin.rb:16:in `new'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/fog-core-2.1.0/lib/fog/storage.rb:22:in `new'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/carrierwave-2.0.0/lib/carrierwave/storage/fog.rb:68:in `eager_load'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/carrierwave-2.0.0/lib/carrierwave.rb:77:in `block in <class:Railtie>'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/activesupport-6.0.0/lib/active_support/lazy_load_hooks.rb:69:in `block in execute_hook'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/activesupport-6.0.0/lib/active_support/lazy_load_hooks.rb:62:in `with_execution_control'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/activesupport-6.0.0/lib/active_support/lazy_load_hooks.rb:67:in `execute_hook'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/activesupport-6.0.0/lib/active_support/lazy_load_hooks.rb:52:in `block in run_load_hooks'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/activesupport-6.0.0/lib/active_support/lazy_load_hooks.rb:51:in `each'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/activesupport-6.0.0/lib/active_support/lazy_load_hooks.rb:51:in `run_load_hooks'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/railties-6.0.0/lib/rails/application/finisher.rb:118:in `block in <module:Finisher>'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/railties-6.0.0/lib/rails/initializable.rb:32:in `instance_exec'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/railties-6.0.0/lib/rails/initializable.rb:32:in `run'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/railties-6.0.0/lib/rails/initializable.rb:61:in `block in run_initializers'
  /home/user/.rbenv/versions/2.6.3/lib/ruby/2.6.0/tsort.rb:228:in `block in tsort_each'
  /home/user/.rbenv/versions/2.6.3/lib/ruby/2.6.0/tsort.rb:350:in `block (2 levels) in each_strongly_connected_component'
  /home/user/.rbenv/versions/2.6.3/lib/ruby/2.6.0/tsort.rb:431:in `each_strongly_connected_component_from'
  /home/user/.rbenv/versions/2.6.3/lib/ruby/2.6.0/tsort.rb:349:in `block in each_strongly_connected_component'
  /home/user/.rbenv/versions/2.6.3/lib/ruby/2.6.0/tsort.rb:347:in `each'
  /home/user/.rbenv/versions/2.6.3/lib/ruby/2.6.0/tsort.rb:347:in `call'
  /home/user/.rbenv/versions/2.6.3/lib/ruby/2.6.0/tsort.rb:347:in `each_strongly_connected_component'
  /home/user/.rbenv/versions/2.6.3/lib/ruby/2.6.0/tsort.rb:226:in `tsort_each'
  /home/user/.rbenv/versions/2.6.3/lib/ruby/2.6.0/tsort.rb:205:in `tsort_each'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/railties-6.0.0/lib/rails/initializable.rb:60:in `run_initializers'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/railties-6.0.0/lib/rails/application.rb:363:in `initialize!'
  /var/www/app/releases/20191008231529/config/environment.rb:5:in `<top (required)>'
  config.ru:4:in `require_relative'
  config.ru:4:in `block in <main>'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/rack-2.0.7/lib/rack/builder.rb:55:in `instance_eval'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/rack-2.0.7/lib/rack/builder.rb:55:in `initialize'
  config.ru:1:in `new'
  config.ru:1:in `<main>'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/unicorn-5.5.1/lib/unicorn.rb:54:in `eval'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/unicorn-5.5.1/lib/unicorn.rb:54:in `block in builder'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/unicorn-5.5.1/lib/unicorn/http_server.rb:794:in `build_app!'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/unicorn-5.5.1/lib/unicorn/http_server.rb:141:in `start'
  /var/www/app/shared/bundle/ruby/2.6.0/gems/unicorn-5.5.1/bin/unicorn:128:in `<top (required)>'
  /var/www/app/shared/bundle/ruby/2.6.0/bin/unicorn:23:in `load'
  /var/www/app/shared/bundle/ruby/2.6.0/bin/unicorn:23:in `<top (required)>'

1,2行目のfogに関するエラーについて
config/initializers/carrier_wave.rbにてAWSの設定を行っています。
各値はdotenvというGemを使って環境変数に設定しています。
VPSにはconfig/master.keyを作成し、ローカルと同じ値を設定しました。

3行目以降のエラーについて
UnicornはGemfileのgem 'unicorn'で入るはずだと思うんですが…
一応、VPSでgem install unicornを実行してから再デプロイするも状況変わらず。

CapistranoやらUnicornやらNginxやら初めてのことばかりでよくわかっていないので、どなたか解決法を教えていただけると大変助かります。