Another error when stopping 3+ containers:

ufw-docker-automated: Deleting rule: /usr/bin/sudo ufw route delete deny from 172.17.0.5 to any comment upbeat_antonelli:7e9a1537a501
ufw: Rule deleted

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x68 pc=0x7b849c]

goroutine 23 [running]:
main.handleUfwRule(0xc000082660)
        /home/ubuntu/ufw-docker-automated/main.go:50 +0x13c
created by main.main
        /home/ubuntu/ufw-docker-automated/main.go:238 +0xb4

Found the reason. On this line I'm trying to reference container's IP address from *types.NetworkSettings field. But it's returning empty string when I turn off multiple containers at once. I guess this IPAddress field is trying to get the IP address after container is already detached from the network, hence IPAddress is empty.
Since ContainerIP variable is emptry next if condition gets triggered and program crashes because of unsafe map access.

Ultimately this reveals the bigger problem that I cannot get the IPAddress reference before container shuts down. I need to store the container IP address somewhere else.