Group id missing (NaN) when REST calls for epics are made in the new boards sidebar.

Summary

(ONLY APPLICABLE TO PROJECT BOARDS with EPIC SWIMLANES) Group id missing (NaN) when REST calls for epics are made in the new boards sidebar.

Example Project

https://gitlab.com/gitlab-org/gitlab/-/boards/2262598?scope=all&utf8=%E2%9C%93&label_name[]=devops%3A%3Aplan&author_username=euko&group_by=epic

Try using the epic dropdown for euko's issue (for testing - please ignore) gitlab-org/gitlab#297373

Relevant logs and/or screenshots

Cause

groupId, required to do graphql queries/mutations, is missing in project boards

Possible fixes

!55954 (merged)