[server][test][FaceRestAction] fix broken test caused by DBAgent specification changing

Before commit eb1562019e5c5659a5b5e20b9c51031cc6a884f0 and
6bac1ebe4b7aad806c8b648133027b9bbb3afb6e, DBAgent::UpdateArg::agg cannot
treat NULL value.
So, it cannot update column with NULL.

After these commit, DBAgent::UpdateArg::add can treat NULL value.
So, it can update column with NULL.