The word 'undefined' appears at the bottom of error pages (see https://bookbrainz.org/not-a-path for example), suggesting that the React template is outputting the value of a variable that is undefined.

The issue comes from the file src/server/templates/target.js, where the template `props && script && …` need to be changed to verify if the `props` and `script` variables are null or undefined, and only if that is not the case, add the following `<script ...`