Fix EventLogging of responses when correct is null

If you want EventLogging to record NULL for a boolean field, you
can't pass null for the value. Instead, you have to not pass the
property at all.

Change-Id: I7c28f9f7b709a861a775b60f2d762ce57317768b
(cherry picked from commit 838c2b09310b699b6588346f2e9d07ede2e6f9d8)