systemd cannot generate a service unit for init script, which is a symbolic link to a file in another local partition

Issue

• I created a init script in /opt, which is another local partition. And, I created a symbolic link in /etc/init.d to the file.
• I noticed a bug in Red Hat Enterprise Linux 7.2 of https://access.redhat.com/solutions/2067013. And, I updated the systemd package.
• But, after reboot, I found that systemd didn't generate a service for my init script.