go: cmd/godoc: confused by symlinks in GOROOT: godoc: corpus fstree is nil

Please answer these questions before submitting your issue. Thanks!

1. What version of Go are you using (go version)? go version go1.6 linux/amd64
2. What operating system and processor architecture are you using (go env)? GOARCH=“amd64” GOBIN=“” GOEXE=“” GOHOSTARCH=“amd64” GOHOSTOS=“linux” GOOS=“linux” GOPATH=“/home/me/Code/go” GORACE=“” GOROOT=“/usr/lib/go” GOTOOLDIR=“/usr/lib/go/pkg/tool/linux_amd64” GO15VENDOREXPERIMENT=“1” CC=“gcc” GOGCCFLAGS=“-fPIC -m64 -pthread -fmessage-length=0” CXX=“g++” CGO_ENABLED=“1”
3. What did you do? go get golang.org/x/tools/cmd/godoc sudo -E go install golang.org/x/tools/cmd/godoc godoc -http=":8080"
4. What did you expect to see? godoc running on the command line, listening to HTTP requests
5. What did you see instead? “2016/03/31 11:15:45 godoc: corpus fstree is nil”, followed by program exit with status code -1
6. Other notes
   • It was working when I was running go 1.5, I added the ubuntu-lxc/lxd-stable ppa and upgraded to go 1.6.
   • I tried running go get with --update, and then tried removing all references I could find to godoc and the installing again using the commands from question # 3.
   • which godoc gives “/usr/lib/go/bin/godoc”
   • godoc net/http prints the documentation on the command line, as expected.