[Ruby on Rails 6] error Command "webpack" not found.

http://localhost:3000/pages/home へアクセスしようとしたところエラーが起きてしまいました

=> Booting Puma
=> Rails 6.0.3.4 application starting in development 
=> Run `rails server --help` for more startup options
Puma starting in single mode...
* Version 4.3.6 (ruby 2.6.3-p62), codename: Mysterious Traveller
* Min threads: 5, max threads: 5
* Environment: development
* Listening on tcp://127.0.0.1:3000
* Listening on tcp://[::1]:3000
Use Ctrl-C to stop
Started GET "/pages/home" for ::1 at 2020-11-05 11:54:47 +0900
   (1.7ms)  SELECT sqlite_version(*)
Processing by PagesController#home as HTML
  Rendering pages/home.html.erb within layouts/application
  Rendered pages/home.html.erb within layouts/application (Duration: 2.8ms | Allocations: 209)
[Webpacker] Compiling...
[Webpacker] Compilation failed:
yarn run v1.22.10
info Visit https://yarnpkg.com/en/docs/cli/run for documentation about this command.


error Command "webpack" not found.

Completed 500 Internal Server Error in 1396ms (ActiveRecord: 0.0ms | Allocations: 9768)


  
ActionView::Template::Error (Webpacker can't find application in /Users/sugitakoutarou/photopost/public/packs/manifest.json. Possible causes:
1. You want to set webpacker.yml value of compile to true for your environment
   unless you are using the `webpack -w` or the webpack-dev-server.
2. webpack has not yet re-run to reflect updates.
3. You have misconfigured Webpacker's config/webpacker.yml file.
4. Your webpack configuration is not creating a manifest.
Your manifest contains:
{
}
):
     6:     <%= csp_meta_tag %>
     7: 
     8:     <%= stylesheet_link_tag 'application', media: 'all', 'data-turbolinks-track': 'reload' %>
     9:     <%= javascript_pack_tag 'application', 'data-turbolinks-track': 'reload' %>
    10:   </head>
    11: 
    12:   <body>
  
app/views/layouts/application.html.erb:9