Logging MacBook firewall is empty
Solution 1:
To get some logging from the Firewall you have to define some rules.
Open System Preferences > Security & Privacy > Firewall, unlock it, and select
Firewall Options and add some rules about application you want to block any access from the outside.
Ex. :
Once done, lock back the Security & Privacy preference menu.
Try any prohibited or allowed access and you will see it appear in /var/log/appfirewall.log.