[XDCR] panic thrown in backfill_manager

[2020-10-18 13:49:10,069] - [xdcrnewbasetests:3599] INFO - panic: runtime error: invalid memory address or nil pointer dereference
[2020-10-18 13:49:10,069] - [xdcrnewbasetests:3599] INFO - [signal SIGSEGV: segmentation violation code=0x1 addr=0x20 pc=0x9b6df1]
[2020-10-18 13:49:10,069] - [xdcrnewbasetests:3599] INFO -
[2020-10-18 13:49:10,069] - [xdcrnewbasetests:3599] INFO - goroutine 243 [running]:
[2020-10-18 13:49:10,069] - [xdcrnewbasetests:3599] INFO - github.com/couchbase/goxdcr/pipeline_svc.(*PipelineSupervisor).OnEvent(0xc001a762d0, 0xc0030b3400)
[2020-10-18 13:49:10,069] - [xdcrnewbasetests:3599] INFO - /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/goxdcr/pipeline_svc/pipeline_supervisor.go:271 +0x8b1
[2020-10-18 13:49:10,069] - [xdcrnewbasetests:3599] INFO - github.com/couchbase/goxdcr/backfill_manager.(*BackfillRequestHandler).Attach.func1(0xddee40, 0xc003a18ba0)
[2020-10-18 13:49:10,069] - [xdcrnewbasetests:3599] INFO - /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/goxdcr/backfill_manager/backfill_request_handler.go:580 +0xe8
[2020-10-18 13:49:10,069] - [xdcrnewbasetests:3599] INFO - github.com/couchbase/goxdcr/backfill_manager.(*BackfillRequestHandler).handleVBDone(0xc0004cec60, 0xb9f2a0, 0xc0010d7c50, 0xc004089b60, 0xc004089bc0, 0xddee40, 0xc0001b79c0)
[2020-10-18 13:49:10,070] - [xdcrnewbasetests:3599] INFO - /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/goxdcr/backfill_manager/backfill_request_handler.go:474 +0x362
[2020-10-18 13:49:10,070] - [xdcrnewbasetests:3599] INFO - github.com/couchbase/goxdcr/backfill_manager.(*BackfillRequestHandler).run(0xc0004cec60)
[2020-10-18 13:49:10,070] - [xdcrnewbasetests:3599] INFO - /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/goxdcr/backfill_manager/backfill_request_handler.go:217 +0xa60
[2020-10-18 13:49:10,070] - [xdcrnewbasetests:3599] INFO - created by github.com/couchbase/goxdcr/backfill_manager.(*BackfillRequestHandler).Start.func1
[2020-10-18 13:49:10,070] - [xdcrnewbasetests:3599] INFO - /home/couchbase/jenkins/workspace/couchbase-server-unix/goproj/src/github.com/couchbase/goxdcr/backfill_manager/backfill_request_handler.go:125 +0xa3
[2020-10-18 13:49:10,070] - [xdcrnewbasetests:3599] INFO - 2020-10-18T13:48:47.398-07:00 INFO GOXDCR.ReplMgr: GOMAXPROCS=4
[2020-10-18 13:49:10,070] - [xdcrnewbasetests:3599] INFO - 2020-10-18T13:48:47.401-07:00 INFO GOXDCR.AuditSvc: Created audit service.
[2020-10-18 13:49:10,070] - [xdcrnewbasetests:3599] INFO - 2020-10-18T13:48:47.401-07:00 INFO GOXDCR.UILogSvc: Created ui log service.
[2020-10-18 13:49:10,070] - [xdcrnewbasetests:3599] INFO - 2020-10-18T13:48:47.915-07:00 INFO GOXDCR.RemClusterSvc: Agent

Test:

./testrunner -i /tmp/testexec.15187.ini -p get-cbcollect-info=False,get-cbcollect-info=False -t xdcr.lww.Lww.test_replication_with_lww_default,items=1000