Cannot read properties of undefined (reading 'name') when antora.yml is empty

After following the Antora documentation, I have a playbook repository (https://gitlab.com/namespace/antora-playbook.git) that looks like this:

├── package-lock.json
├── package.json
└── playbook.yml

And a content repository (https://gitlab.com/namespace/antora-example.git) that looks like this:

├── antora.yml
├── modules
│   └── ROOT
│       └── pages
│           └── index.adoc
├── package-lock.json
└── package.json

My playbook.yml file looks like this:

site:
  title: Demo Site
  url: https://demo-site.com
content:
  sources:
  - url: https://gitlab.com/namespace/antora-example.git
    branches: [main] <-- tried without the brackets as well.
ui:
  bundle:
    url: https://gitlab.com/antora/antora-ui-default/-/jobs/artifacts/HEAD/raw/build/ui-bundle.zip?job=bundle-stable
    snapshot: true

My antora.yml file looks like this:

name: demo-site
title: Demo Site
version: 'v1.0'
display_version: 'Version 1.0'

I installed Antora according to the documentation using Node 16.20.2 and included this configuration in my package.json from your security notice:

{
  "overrides": {
    "vinyl-fs": {
      "glob-stream": "~7.0"
    }
  },
  "devDependencies": {
    "@antora/cli": "3.1.7",
    "@antora/site-generator": "3.1.7"
  }
}

The problem is, when I run npx antora playbook.yml I get the following error:

Cannot read properties of undefined (reading 'name') in https://gitlab.com/namespace/antora-example.git (branch: main)

Here's the stacktrace:

Cause: TypeError
        at loadComponentDescriptor (/antora-playbook/node_modules/@antora/content-aggregator/lib/aggregate-content.js:695:12)
        at /antora-playbook/node_modules/@antora/content-aggregator/lib/aggregate-content.js:442:52
        at async collectFilesFromStartPaths (/antora-playbook/node_modules/@antora/content-aggregator/lib/aggregate-content.js:431:18)
        at async Promise.all (index 0)
        at async Promise.all (index 0)
        at async generateSite (/antora-playbook/node_modules/@antora/site-generator/lib/generate-site.js:23:5)
        at async Command.parseAsync (/antora-playbook/node_modules/commander/lib/command.js:935:5)