Starting strapi in develop ends in undefinied 'toLowerCase' TypeError

System Information
  • Strapi Version: 4.0.7
  • Operating System: Linux/Ubuntu 20
  • Database: MariaDB
  • Node Version: v14.18.1
  • NPM Version: 6.14.15
  • Yarn Version: 1.22.15

If i start strapi with yarn develop, I get the following error:

⛔️ Server wasn't able to start properly.
[2022-02-05 14:40:45.311] error: Cannot read property 'toLowerCase' of undefined
TypeError: Cannot read property 'toLowerCase' of undefined

Does anyone have an idea what this could be?

Thanks!