PostCSS config, plugins as an object (as opposed to an array) fails

With the following postcss.config.js:

module.exports = {
  plugins: {
    tailwindcss: {},
    autoprefixer: {},
  },
};

This gem fails with the following message:

Configuration file: /Users/foo/project/_config.yml
            Source: /Users/foo/project
       Destination: /Users/foo/project/_site
 Incremental build: disabled. Enable with --incremental
      Generating...
PostCSS Server listening on port 8124...
/Users/foo/project/node_modules/postcss/lib/processor.js:60
        throw new Error(i + ' is not a PostCSS plugin')
        ^

Error: [object Object] is not a PostCSS plugin
    at Processor.normalize (/Users/foo/project/node_modules/postcss/lib/processor.js:60:15)
    at new Processor (/Users/foo/project/node_modules/postcss/lib/processor.js:9:25)
    at postcss (/Users/foo/project/node_modules/postcss/lib/postcss.js:25:10)
    at Function.process (/Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-postcss-0.4.0/bin/postcss:9:5)
    at Socket.<anonymous> (/Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-postcss-0.4.0/bin/postcss:21:14)
    at Socket.emit (events.js:314:20)
    at addChunk (_stream_readable.js:297:12)
    at readableAddChunk (_stream_readable.js:272:9)
    at Socket.Readable.push (_stream_readable.js:213:10)
    at TCP.onStreamRead (internal/stream_base_commons.js:188:23)
  Conversion error: Jekyll::Converters::PostCss encountered an error while converting 'styles.css':
                    undefined method `chomp' for nil:NilClass
                    ------------------------------------------------
      Jekyll 4.2.0   Please append `--trace` to the `serve` command
                     for any additional information or backtrace.
                    ------------------------------------------------
Traceback (most recent call last):
	43: from /Users/ali/.rbenv/versions/2.7.2/bin/bundle:23:in `<main>'
	42: from /Users/ali/.rbenv/versions/2.7.2/bin/bundle:23:in `load'
	41: from /Users/ali/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.14/exe/bundle:37:in `<top (required)>'
	40: from /Users/ali/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.14/lib/bundler/friendly_errors.rb:130:in `with_friendly_errors'
	39: from /Users/ali/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.14/exe/bundle:49:in `block in <top (required)>'
	38: from /Users/ali/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.14/lib/bundler/cli.rb:24:in `start'
	37: from /Users/ali/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.14/lib/bundler/vendor/thor/lib/thor/base.rb:485:in `start'
	36: from /Users/ali/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.14/lib/bundler/cli.rb:30:in `dispatch'
	35: from /Users/ali/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.14/lib/bundler/vendor/thor/lib/thor.rb:392:in `dispatch'
	34: from /Users/ali/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.14/lib/bundler/vendor/thor/lib/thor/invocation.rb:127:in `invoke_command'
	33: from /Users/ali/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.14/lib/bundler/vendor/thor/lib/thor/command.rb:27:in `run'
	32: from /Users/ali/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.14/lib/bundler/cli.rb:494:in `exec'
	31: from /Users/ali/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.14/lib/bundler/cli/exec.rb:28:in `run'
	30: from /Users/ali/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.14/lib/bundler/cli/exec.rb:63:in `kernel_load'
	29: from /Users/ali/.rbenv/versions/2.7.2/lib/ruby/gems/2.7.0/gems/bundler-2.2.14/lib/bundler/cli/exec.rb:63:in `load'
	28: from /Users/foo/project/vendor/bundle/ruby/2.7.0/bin/jekyll:23:in `<top (required)>'
	27: from /Users/foo/project/vendor/bundle/ruby/2.7.0/bin/jekyll:23:in `load'
	26: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/exe/jekyll:15:in `<top (required)>'
	25: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/mercenary-0.4.0/lib/mercenary.rb:21:in `program'
	24: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/mercenary-0.4.0/lib/mercenary/program.rb:44:in `go'
	23: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/mercenary-0.4.0/lib/mercenary/command.rb:221:in `execute'
	22: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/mercenary-0.4.0/lib/mercenary/command.rb:221:in `each'
	21: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/mercenary-0.4.0/lib/mercenary/command.rb:221:in `block in execute'
	20: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/commands/serve.rb:86:in `block (2 levels) in init_with_program'
	19: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/command.rb:91:in `process_with_graceful_fail'
	18: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/command.rb:91:in `each'
	17: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/command.rb:91:in `block in process_with_graceful_fail'
	16: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/commands/build.rb:36:in `process'
	15: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/commands/build.rb:65:in `build'
	14: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/command.rb:28:in `process_site'
	13: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/site.rb:80:in `process'
	12: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/site.rb:211:in `render'
	11: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/site.rb:538:in `render_pages'
	10: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/site.rb:538:in `each'
	 9: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/site.rb:539:in `block in render_pages'
	 8: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/site.rb:547:in `render_regenerated'
	 7: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/renderer.rb:63:in `run'
	 6: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/renderer.rb:84:in `render_document'
	 5: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/renderer.rb:104:in `convert'
	 4: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/renderer.rb:104:in `reduce'
	 3: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/renderer.rb:104:in `each'
	 2: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-4.2.0/lib/jekyll/renderer.rb:106:in `block in convert'
	 1: from /Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-postcss-0.4.0/lib/jekyll/converters/postcss.rb:41:in `convert'
/Users/foo/project/vendor/bundle/ruby/2.7.0/gems/jekyll-postcss-0.4.0/lib/jekyll-postcss/socket.rb:28:in `read': undefined method `chomp' for nil:NilClass (NoMethodError)
error: Script failed: see failed command above

However this syntax works as expected:

module.exports = {
  plugins: [
    require('tailwindcss'),
    require('autoprefixer'),
  ],
};

Start with lib/jekyll-postcss/socket.rb and lib/jekyll/converters/postcss.rb, then inspect bin/postcss where the stack trace shows configuration is passed to PostCSS. Reproduce the issue with the object-form postcss.config.js and verify that the Jekyll build succeeds while the existing array-form configuration continues to work.