The treatment of the newly-introduced RFC 1918 automatic empty zones is subtly different on 9.9.
In BIND 9.6-ESV-R5, 9.7.4, 9.8.1 (and newer versions of 9.6-ESV, 9.7 and 9.8 that supersede them), all of the empty zones except the new RFC 1918 empty zones are added automatically when empty-zones-enable has not been declared as an option. These new RFC 1918 empty zones will not be loaded unless named.conf explicitly includes option empty-zones-enable yes; (i.e,
the default is 'yes', but not fully 'yes'. This was done to minimize
the likelihood of unexpected behaviour being encountered by users
following small incremental upgrades within the same major version.)
From BIND 9.9.0, the new RFC 1918 empty zones have equal status with those in the earlier set and are all included by default.