[FIX] Hooks now correctly check if counterside implemented hook

All hooks now expect to see null values

Change-Id: Ieabc1f226a27b184ff91a9349bbc62a1ec0094b9
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1685
Tested-by: Jenkins CI
Reviewed-by: Arndt Lasarzik <alasarzik@gmail.com>
Reviewed-by: Franz Zieris <zieris@inf.fu-berlin.de>