Conditional update method from the persistent OVO class is blindly
relying on persistent OVOs having an OPTIONAl_FIELDS attribute without
defining a default.
This patch adds an empty default so we can do conditional updates on
persistent OVO instances that don't have optional fields.
Change-Id: Icf640da34df0990b5ad2609d5d230ac9b0a51311
(cherry picked from commit 2987b33970)