CI (unstable): Panic from memdb skiplist - invalid memory address or nil pointer dereference

Unstable CI Failure in run - http://ci2i-unstable.northscale.in/sherlock-12.10-11.35.fail.html

Test case:
=== RUN TestFieldsWithSpecialCharacters
2015/10/12 12:14:35 In TestFieldsWithSpecialCharacters()
2015-10-12T12:14:37.01Z+05:30 [Error] WatcherServer.runOnce() : Watcher terminated unexpectedly.
— FAIL: TestFieldsWithSpecialCharacters (1.36s)
common_test.go:90: Error in creating the index: Terminate Request due to server termination

From indexer logs:

2015-10-12T12:14:36.675Z+05:30 [Info] MemDBSlice Slice Id 0, IndexInstId 0x54cbd0 created ondisk snapshot /opt/build/ns_server/data/n_1/data/@2i/default_index_userscreenname_9854518389345554326_0.index/snapshot.0000000002. Took 1.347089ms
2015-10-12T12:14:36.675Z+05:30 [Info] MemDBSlice Slice Id 0, IndexInstId 0x54cbd0 created ondisk snapshot /opt/build/ns_server/data/n_1/data/@2i/default_index_city_828140782223835805_0.index/snapshot.0000000002. Took 1.555333ms
panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x871d1e]

goroutine 670300 [running]:
github.com/couchbase/indexing/secondary/memdb/skiplist.(*Node).dcasNext(0x0, 0x5, 0x0, 0xc22417c8a0, 0xc232200000, 0x1)
/opt/build/goproj/src/github.com/couchbase/indexing/secondary/memdb/skiplist/skiplist.go:123 +0x12e
github.com/couchbase/indexing/secondary/memdb/skiplist.(*Skiplist).Insert3(0xc223b317c0, 0x7f018472cd98, 0xc23220b420, 0xc21ebbf8b0, 0xc22442f830, 0x5, 0x0, 0x0)
/opt/build/goproj/src/github.com/couchbase/indexing/secondary/memdb/skiplist/skiplist.go:259 +0x4c2
github.com/couchbase/indexing/secondary/memdb.(*Writer).Upsert2(0xc21ed0bf00, 0xc23220b420, 0x1668280, 0x0)
/opt/build/goproj/src/github.com/couchbase/indexing/secondary/memdb/memdb.go:195 +0x296
github.com/couchbase/indexing/secondary/indexer.(*memdbSlice).insertSecIndex(0xc221dcc9a0, 0xc237b5f590, 0x26, 0x30, 0xc231d08c20, 0x18, 0x18, 0x1)
/opt/build/goproj/src/github.com/couchbase/indexing/secondary/indexer/memdb_slice_impl.go:308 +0x51f
github.com/couchbase/indexing/secondary/indexer.(*memdbSlice).insert(0xc221dcc9a0, 0xc237b5f590, 0x26, 0x30, 0xc231d08c20, 0x18, 0x18, 0x1)
/opt/build/goproj/src/github.com/couchbase/indexing/secondary/indexer/memdb_slice_impl.go:255 +0xbc
github.com/couchbase/indexing/secondary/indexer.(*memdbSlice).handleCommandsWorker(0xc221dcc9a0, 0x1)
/opt/build/goproj/src/github.com/couchbase/indexing/secondary/indexer/memdb_slice_impl.go:222 +0x49c
created by github.com/couchbase/indexing/secondary/indexer.NewMemDBSlice
/opt/build/goproj/src/github.com/couchbase/indexing/secondary/indexer/memdb_slice_impl.go:159 +0xa8e

Logs:
http://ci2i-unstable.northscale.in/logs-12.10-11.35.tar.gz