[Bug] safeline-chaos fails update with the following issue server.go:83

What happened?

panic: runtime error: invalid memory address or nil pointer dereference goroutine ... running: git.in.chaitin.net/safeline-ce/challenge/server.(*APIServer).Shutdown(0xc000... ) /app/server/server.go:83 +0xdb main.gracefulShutdown(...)

How we reproduce?

1. ...attempt container update this error is produced each time
2. ...
3. ...

Expected behavior

No response

Error log

panic: runtime error: invalid memory address or nil pointer dereference goroutine ... running: git.in.chaitin.net/safeline-ce/challenge/server.(*APIServer).Shutdown(0xc000... ) /app/server/server.go:83 +0xdb main.gracefulShutdown(...)