Developer credits
Git commits in Moodle 3.7.0 by Justus Dieckmann
commit 8516febdd7c11fc8d399765e821d35db7eff349e Author: Justus Dieckmann <justusdieckmann@wwu.de> Date: Fri, 21 Dec 2018 03:19:38 +0800 Tag: v3.7.0-beta MDL-58256 group: prevents users to be added to a group twice