Automatic merge from branch-5.1

* origin/branch-5.1:
  SONAR-6566 Unable to deliver notifications on MySQL

diff --cc server/sonar-server/src/main/java/org/sonar/server/notifications/NotificationService.java
Simple merge

diff --cc server/sonar-server/src/test/java/org/sonar/server/notifications/NotificationServiceTest.java
Simple merge