unit: add uniary missing checks (#2412)
unit: add uniary missing checks (#2412)

* validated the result when checking for not null or not missing with  function.
couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios,couchbase/couchbase-lite-ios