Index Page not shown when only unlisted documents are present

[lebalz]

Have you read the Contributing Guidelines on issues?

• I have read the Contributing Guidelines on issues.

Prerequisites

• I'm using the latest version of Docusaurus.
• I have tried the npm run clear or yarn clear command.
• I have tried rm -rf node_modules yarn.lock package-lock.json and re-installing packages.
• I have tried creating a repro with https://new.docusaurus.io.
• I have read the console error message carefully (if applicable).

Description

The index page is not listed, when the folder only contains unlisted documents.

docs
├── test
    ├── index.md                // unlisted=false
    └── unlisted-doc.md         // unlisted=true

I'd expect that the index.md would be displayed as the category page.

The issue happens only when the site is built and served in production.

Reproducible demo

https://codesandbox.io/p/devbox/old-bush-9jlkhj

Steps to reproduce

1. build the site
2. serve the site and see that the test-directory is not displayed.

Expected behavior

the test directory should be listed

Actual behavior

the test directory is not displayed

Your environment

• Public source code:
• Public site URL:
• Docusaurus version used:
• Environment name and version (e.g. Chrome 89, Node.js 16.4):
• Operating system and version (e.g. Ubuntu 20.04.2 LTS):

Self-service

• I'd be willing to fix this bug myself.