Merge branch 'stable-2.15' into stable-2.16

* stable-2.15:
  ReplicationQueue: Check nulls in firePendingEvents
  Log stack trace when an error occur while deleting event
  Append LF to the json string of persisted replication event
  Change default for the replicateOnStartup to false
  Don't lose ref-updated events on plugin restart

Change-Id: Icc855dd26ee9f8fb195435d8902404b364242940