Unable to build the site using bundle exec middleman build --build-dir docs

[TheSpartan1980]

RVM Version: 1.29.1 (latest)
Ruby: 2.7.2p137
macOS: 11.4 Big Sur

As part of the PR to update the Docker tutorial I tried to build the site using the recommended command in the building site section of the CONTRIBUTING.md

When running the command bundle exec middleman build --build-dir docs I encountered the following error:

/Users/carlosguti/.rvm/gems/ruby-2.7.2/gems/middleman-core-4.3.11/lib/middleman-core/builder.rb:232: warning: URI.escape is obsolete
/Users/carlosguti/.rvm/gems/ruby-2.7.2/gems/middleman-core-4.3.11/lib/middleman-core/builder.rb:232: warning: URI.escape is obsolete
/Users/carlosguti/.rvm/gems/ruby-2.7.2/gems/middleman-core-4.3.11/lib/middleman-core/builder.rb:232: warning: URI.escape is obsolete
DEPRECATION WARNING: autoprefixer-rails was deprected. Migration guide:
https://github.com/ai/autoprefixer-rails/wiki/Deprecated (called from load at /Users/carlosguti/.rvm/gems/ruby-2.7.2/bin/middleman:23)
DEPRECATION WARNING: autoprefixer-rails was deprected. Migration guide:
https://github.com/ai/autoprefixer-rails/wiki/Deprecated (called from load at /Users/carlosguti/.rvm/gems/ruby-2.7.2/bin/middleman:23)
DEPRECATION WARNING: autoprefixer-rails was deprected. Migration guide:
https://github.com/ai/autoprefixer-rails/wiki/Deprecated (called from load at /Users/carlosguti/.rvm/gems/ruby-2.7.2/bin/middleman:23)
TypeError: Cannot read property 'version' of undefined
TypeError: Cannot read property 'version' of undefined
       error  docs/stylesheets/highlighting.css
       error  docs/stylesheets/site.css
TypeError: Cannot read property 'version' of undefined
       error  docs/stylesheets/material.css
   identical  docs/images/github.png
   identical  docs/mstile-310x150.png
   identical  docs/favicon-196x196.png
   identical  docs/apple-touch-icon.png
   identical  docs/apple-touch-icon-57x57-precomposed.png
   identical  docs/favicon-160x160.png
   identical  docs/images/kitchen_terraform_logo.png
   identical  docs/apple-touch-icon-precomposed.png
   identical  docs/favicon-96x96.png
   identical  docs/favicon-32x32.png
   identical  docs/favicon.png
   identical  docs/mstile-70x70.png
   identical  docs/favicon-16x16.png
   identical  docs/mstile-310x310.png
   identical  docs/mstile-150x150.png
   identical  docs/mstile-144x144.png
   identical  docs/apple-touch-icon-180x180-precomposed.png
   identical  docs/apple-touch-icon-144x144-precomposed.png
   identical  docs/apple-touch-icon-120x120-precomposed.png
   identical  docs/apple-touch-icon-152x152-precomposed.png
   identical  docs/apple-touch-icon-72x72-precomposed.png
/Users/carlosguti/.rvm/gems/ruby-2.7.2/gems/middleman-core-4.3.11/lib/middleman-core/builder.rb:232: warning: URI.escape is obsolete
/Users/carlosguti/.rvm/gems/ruby-2.7.2/gems/middleman-core-4.3.11/lib/middleman-core/builder.rb:232: warning: URI.escape is obsolete
   identical  docs/apple-touch-icon-114x114-precomposed.png
   identical  docs/apple-touch-icon-76x76-precomposed.png
/Users/carlosguti/.rvm/gems/ruby-2.7.2/gems/middleman-core-4.3.11/lib/middleman-core/builder.rb:232: warning: URI.escape is obsolete
   identical  docs/images/copado_logo.png
   identical  docs/apple-touch-icon-60x60-precomposed.png
/Users/carlosguti/.rvm/gems/ruby-2.7.2/gems/middleman-core-4.3.11/lib/middleman-core/builder.rb:232: warning: URI.escape is obsolete
   identical  docs/favicon.ico
/Users/carlosguti/.rvm/gems/ruby-2.7.2/gems/middleman-core-4.3.11/lib/middleman-core/builder.rb:232: warning: URI.escape is obsolete
/Users/carlosguti/.rvm/gems/ruby-2.7.2/gems/middleman-core-4.3.11/lib/middleman-core/builder.rb:232: warning: URI.escape is obsolete
/Users/carlosguti/.rvm/gems/ruby-2.7.2/gems/middleman-core-4.3.11/lib/middleman-core/builder.rb:232: warning: URI.escape is obsolete
/Users/carlosguti/.rvm/gems/ruby-2.7.2/gems/middleman-core-4.3.11/lib/middleman-core/builder.rb:232: warning: URI.escape is obsolete
   identical  docs/about.html
/Users/carlosguti/.rvm/gems/ruby-2.7.2/gems/middleman-core-4.3.11/lib/middleman-core/builder.rb:232: warning: URI.escape is obsolete
   identical  docs/community/index.html
/Users/carlosguti/.rvm/gems/ruby-2.7.2/gems/middleman-core-4.3.11/lib/middleman-core/builder.rb:232: warning: URI.escape is obsolete
   identical  docs/tutorials/index.html
/Users/carlosguti/.rvm/gems/ruby-2.7.2/gems/middleman-core-4.3.11/lib/middleman-core/builder.rb:232: warning: URI.escape is obsolete
   identical  docs/tutorials/openstack_provider.html
/Users/carlosguti/.rvm/gems/ruby-2.7.2/gems/middleman-core-4.3.11/lib/middleman-core/builder.rb:232: warning: URI.escape is obsolete
   identical  docs/tutorials/docker_provider.html
   identical  docs/tutorials/amazon_provider_ec2.html
   identical  docs/javascripts/site.js
   identical  docs/browserconfig.xml
   identical  docs/images/.keep
   identical  docs/tutorials/extensive_kitchen_terraform.html
   identical  docs/index.html
   identical  docs/getting_started.html
There were errors during this build, re-run with `middleman build --verbose` to see the full exception.