second argument of get() is optional

Change-Id: I0c70a885458d673e0706784f7e1df642a1391278
Reviewed-on: http://review.couchbase.org/24302
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>