fluidtypo3.org: Appendig > Migration > To Flux 7.1: Content Element has no rendering definition!

The migration guide to flux 7.1 does not show the documentation but an error:

> ERROR: Content Element with uid "150" and type "fluidcontent_content" has no rendering definition!

https://fluidtypo3.org/documentation/templating-manual/appendix/migration/to-flux-71.html

(I don't know this repository is the right place to file this bug; but I did not find a better one)