Panic in MemDB Visitor

panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0x0 pc=0x464d45]

goroutine 6711513 [running]:
panic(0xf0a080, 0xc8200120d0)
/home/couchbase/.cbdepscache/exploded/x86_64/go-1.6/go/src/runtime/panic.go:464 +0x3e6 fp=0xc8239ecd98 sp=0xc8239ecd18
runtime.panicmem()
/home/couchbase/.cbdepscache/exploded/x86_64/go-1.6/go/src/runtime/panic.go:45 +0x49 fp=0xc8239ecdc0 sp=0xc8239ecd98
runtime.sigpanic()
/home/couchbase/.cbdepscache/exploded/x86_64/go-1.6/go/src/runtime/sigpanic_unix.go:24 +0x2ba fp=0xc8239ece10 sp=0xc8239ecdc0
runtime.memmove(0xc8bc029970, 0x0, 0x8)
/home/couchbase/.cbdepscache/exploded/x86_64/go-1.6/go/src/runtime/memmove_amd64.s:143 +0x365 fp=0xc8239ece18 sp=0xc8239ece10
runtime.growslice(0xca4fe0, 0x0, 0x1, 0x1, 0x2, 0x0, 0x0, 0x0)
/home/couchbase/.cbdepscache/exploded/x86_64/go-1.6/go/src/runtime/slice.go:102 +0x2fe fp=0xc8239ece88 sp=0xc8239ece18
github.com/couchbase/indexing/secondary/memdb.(*MemDB).Visitor.func2(0xc9d40421e0, 0xc8308d6940, 0xc8201749a0, 0xc8308d6900, 0xc8308d6920, 0xc97aa83c80, 0xc9096f1500, 0x30, 0x30, 0xc8bf6a9150)
/home/couchbase/jenkins/workspace/watson-unix/goproj/src/github.com/couchbase/indexing/secondary/memdb/memdb.go:744 +0x3f8 fp=0xc8239ecf60 sp=0xc8239ece88
runtime.goexit()
/home/couchbase/.cbdepscache/exploded/x86_64/go-1.6/go/src/runtime/asm_amd64.s:1998 +0x1 fp=0xc8239ecf68 sp=0xc8239ecf60
created by github.com/couchbase/indexing/secondary/memdb.(*MemDB).Visitor
/home/couchbase/jenkins/workspace/watson-unix/goproj/src/github.com/couchbase/indexing/secondary/memdb/memdb.go:763 +0x26a