On a Debian Wheezy, the post install script for the package "mariadb-server-10.0" tries to call "deb-systemd-helper" which is part of the package "init-system-helpers" which isnt mandatory.
On my wheezy systems, i got this error when doing an upgrade of the packages :
Its just a "visual bug" as this command just tries to unmask the Systemd service "mysql.service" so its not breaking anything on non-systemd systems.
Adding a test to check if "deb-systemd-helper" is present on the system before executing the command would be enough.
On Jessie, the package also isnt mandatory but its a dependency on "cron" which is installed by default on most systems.