CBQE-1531: add nulls test

Change-Id: I16d60c6a8c8c9be36ef7ac70cf4e54b145b2fa1c
Reviewed-on: http://review.couchbase.org/29382
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>