util sub-folder is not getting rendered

Given a sub-folder named "util/" beside meta.yaml in the inventory directory. It should be rendered (at least if option --util is used) and should appear with all its files in the target directory (given by --prefix), isn't it?

If this is the case, it's actually not working with my meta.yaml. My renderer-command was:

data_repo_renderer --prefix /WORK/geomar-data/JRA55-do JRA55-do/meta.yaml --util ./util/

Do I have to add "util" somewhere else?