[XDCR] Panic thrown in interface conversion

Seen on build 6.5.0-1622
Host 172.23.104.104

./testrunner -i /tmp/testexec.14960.ini -p stop-on-failure=False,fail_on_errors=1,get-cbcollect-info=True -t xdcr.xdcrTopologyTests.XDCRTopologyTest.load_with_ops,items=10000,rdirection=bidirection,chain_length=3,ctopology=ring,default@C1=filter_expression:C1-key-1,replication_type=xmem,GROUP=P2

2018-11-14T12:50:35.696-08:00 INFO GOXDCR.RemoteClusterChangeListener: Completed remoteClusterChangedCallback called on id = remoteCluster/zNCmdrwxKSnlN12yyBL4HglKmOHwGKdZt0KVI3xXPZ0=

2018-11-14T12:50:35.702-08:00 INFO GOXDCR.UILogSvc: It took 6.99e-07s to call writeUILog_async

2018-11-14T12:50:35.715-08:00 INFO GOXDCR.AdminPort: doCreateReplicationRequest

2018-11-14T12:50:35.716-08:00 INFO GOXDCR.AdminPort: Finished doCreateReplicationRequest call

panic: interface conversion: interface {} is nil, not string

goroutine 69 [running]:

github.com/couchbase/goxdcr/metadata.ReplicationSettingsMap.CloneAndRedact(0xc4261f62a0, 0xc4261f6300)

        goproj/src/github.com/couchbase/goxdcr/metadata/replication_settings.go:530 +0x40f

github.com/couchbase/goxdcr/replication_manager.(*Adminport).doCreateReplicationRequest(0xc4201946c0, 0xc422ef7000, 0x0, 0x0, 0x0)

        goproj/src/github.com/couchbase/goxdcr/replication_manager/adminport.go:409 +0x298

github.com/couchbase/goxdcr/replication_manager.(*Adminport).handleRequest(0xc4201946c0, 0xc422ef7000, 0xc4264ba280, 0xcc39e0, 0xc4264ba280)

        goproj/src/github.com/couchbase/goxdcr/replication_manager/adminport.go:172 +0x1093

github.com/couchbase/goxdcr/replication_manager.(*Adminport).processRequest(0xc4201946c0, 0xc425b05ee0, 0x1, 0x1, 0xcfafc0, 0xc425b05f10)

        goproj/src/github.com/couchbase/goxdcr/replication_manager/adminport.go:136 +0xf5

github.com/couchbase/goxdcr/replication_manager.(*Adminport).(github.com/couchbase/goxdcr/replication_manager.processRequest)-fm(0xc425b05ee0, 0x1, 0x1, 0x1, 0x1)

        goproj/src/github.com/couchbase/goxdcr/replication_manager/adminport.go:69 +0x48

github.com/couchbase/goxdcr/gen_server.(*GenServer).run(0xc4201946d8)

        goproj/src/github.com/couchbase/goxdcr/gen_server/gen_server.go:104 +0x4a4

created by github.com/couchbase/goxdcr/gen_server.(*GenServer).Start_server

        goproj/src/github.com/couchbase/goxdcr/gen_server/gen_server.go:74 +0xba

2018-11-14T12:50:35.807-08:00 INFO GOXDCR.ReplMgr: GOMAXPROCS=4