GODEBUG=http2debug doesn't work

Hey,
I’m trying to get http2 debug output by setting en environment variable of GODEBUG=http2debug=1 and GODEBUG=http2debug=2 but it doesn’t give me any output.

It should be noticed that GODEBUG=gctrace=1 and GODEBUG=http2server=0 for example do work! So I have no idea what I’m doing wrong.

Is the debug output saved to some file or something? Or supposed to be printed to the screen?

I’m using the latest Caddy (straight from git), a clean Ubuntu 18.04 and go version go1.12.6 linux/amd64.