When installing, then removing (not purging) isc-dhcp-server, it leave
a broken apparmor config, leading to the following error:

Jun 05 12:19:02 rpadovani apparmor.systemd[155394]: AppArmor parser
error for /etc/apparmor.d in profile /etc/apparmor.d/usr.sbin.dhcpd at
line 72: Could not open 'dhcpd.d'
Jun 05 12:19:02 rpadovani apparmor.systemd[155458]: AppArmor parser
error for /etc/apparmor.d/usr.sbin.dhcpd in profile
/etc/apparmor.d/usr.sbin.dhcpd at line 72: Could not open 'dhcpd.d
Jun 05 12:19:02 rpadovani apparmor.systemd[155377]: Error: At least
one profile failed to load

It looks like the instruction at
https://salsa.debian.org/debian/isc-dhcp/-/blob/master/debian/apparmor/usr.sbin.dhcpd#L72
should be

#include if exists <dhcpd.d>

to allow the directory to remain empty. (see "#include mechanism" in
the apparmor.d(5) manpage)