Merge branch '1.2.1-patch' into 'master'

Fix ConcurrentModificationException when plugins unload

See merge request !20
Status Job ID Name Coverage
  Build
passed #14345275
job-build

00:00:06

 
  Test
passed #14345276
job-test

00:00:07

 
  Deploy
passed #14345277
job-deploy

00:00:24