engine: findbugs possible null pointer dereference

fix from commit d46ebd8712f369b924e199b82197e59568a686ff

Change-Id: Icb9829514f49cb7f371b31acc018112beda477fb
Bug-Url: https://bugzilla.redhat.com/1051041
Signed-off-by: Shahar Havivi <shaharh@redhat.com>