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

I have a project that doesn't contain a static assets directory. This prevents the Webpack dev server from running due to a misconfiguration of the plugins added by Docusaurus. I was able to workaround this issue by adding a static directory and adding some content to it.

[SUCCESS] Docusaurus website is running at: http://localhost:3000/

[ERROR] TypeError: Cannot read properties of undefined (reading 'constructor')
     at /Users/william.kirby/Code/my-project/node_modules/webpack-dev-server/lib/Server.js:1860:22
     at Array.find (<anonymous>)
     at /Users/william.kirby/Code/my-project/node_modules/webpack-dev-server/lib/Server.js:1859:60
     at Array.forEach (<anonymous>)
     at Server.initialize (/Users/william.kirby/Code/my-project/node_modules/webpack-dev-server/lib/Server.js:1846:17)
     at Server.start (/Users/william.kirby/Code/my-project/node_modules/webpack-dev-server/lib/Server.js:3358:16)
     at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
     at async Command.start (/Users/william.kirby/Code/my-project/node_modules/@docusaurus/core/lib/commands/start/start.js:42:5)
[INFO] Docusaurus version: 3.4.0
Node version: v18.18.0

This appears to be a regression introduced in v3.4.0 by this PR: #9859
The createStaticDirectoriesCopyPlugin function returns undefined when no static directories exist and Webpack isn't able to handle this.

Reproducible demo

No response

Steps to reproduce

1. Go to https://new.docusaurus.io/
2. Create a new Docusaurus project with StackBlitz
3. Kill the development server
4. Delete the static directory
5. Attempt to restart the development server

Expected behavior

I would expect the development server to run even if no static assets exist.

Actual behavior

The development server failed to start.

Your environment

• Docusaurus version used: 3.4
• Environment name and version (e.g. Chrome 89, Node.js 16.4): Node 18.18.0
• Operating system and version (e.g. Ubuntu 20.04.2 LTS): MacOS 14.4.1

Self-service

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