Just tried it and repo creation works again. Thanks for the fix!

But in addition to plain project creation in our Gerrit, we also do the following tasks that are not covered by the plugin:

• create a corresponding repo on GitHub (otherwise replication to GitHub will fail and throw errors),
• setup mirroring from Phabricator (otherwise commit hashes in Phabricator tasks will not automatically get linked), and
• create dedicated project owner groups and adjust them to ease management of project ownership.

In T355644#9502223, @Jdforrester-WMF wrote:

Do we want to do use the "corresponding mirror[s] in Diffusion"?

ping :-)

It seems the repo got added manually. Anyway, I've now:

• set the parent to mediawiki/extensions,
• added a dedicated owner group, and
• created the replication target in GitHub.

The Gerrit repo is ready: https://gerrit.wikimedia.org/r/#/admin/projects/mediawiki/extensions/PlaceNewSection