That form of domain name is very common in DNS configuration. All it means is the name is complete already and should not have any local search domains appended. It's unusual to see it in URLs, but its presence should be harmless; that it's not harmless in Caddy is definitely an error - but I can't begin to understand why it would be seen as a particularly significant one.

The correct way to write a fully qualified domain name is with a period at the end otherwise it’s subject to the resolver search path.

you're right, I have seen the end dot in DNS configuration. I was a bit snarky in my reply.