Developer credits
Git commits in Moodle 3.6.3 by Justus Dieckmann
commit d783d4759c22c4ed1e8f72f832d668069424f71f Author: Justus Dieckmann <justusdieckmann@wwu.de> Date: Fri, 21 Dec 2018 03:19:38 +0800 Tag: v3.6.3 MDL-58256 group: prevents users to be added to a group twice