CBQE-1960: tuq: fix null tests

Change-Id: Idaf018f1537561062d9aad668b5a585403ac5190
Reviewed-on: http://review.couchbase.org/33435
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>