flag: NewFlagSet returns a FlagSet with a nil Usage func

[d3ce1t]

Please answer these questions before submitting your issue. Thanks!

What version of Go are you using (go version)?

go version go1.6.3 darwin/amd64

What operating system and processor architecture are you using (go env)?

Mac OS X 10.11.6
GOARCH="amd64"
GOHOSTARCH="amd64"
GOHOSTOS="darwin"

What did you do?

Create a new flag.FlagSet and call Usage() function.

Please, find the source code related to this issue in the following link: https://play.golang.org/p/_GujXXUvno

What did you expect to see?

Printed information on screen about used flags.

What did you see instead?

Runtime error because of nil pointer dereference

[bradfitz]

It's been like this since Go 1: https://github.com/golang/go/blob/release-branch.go1/src/pkg/flag/flag.go#L785

So, super low priority. Maybe documentation.

/cc @robpike

[gopherbot]

CL https://golang.org/cl/31576 mentions this issue.