Report an error otherwise.
Change-Id: Ia76ea03a3f26b13dd9bca49f7bd42101d1ff1f9e
Reviewed-on: https://go-review.googlesource.com/c/go/+/278475
Trust: Robert Griesemer <gri@golang.org>
Trust: Robert Findley <rfindley@google.com>
Run-TryBot: Robert Griesemer <gri@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Robert Findley <rfindley@google.com>