Previously, the suggested code would result in the following golint warning:
“should drop = 0 from declaration of var errorsOnlyKey; it is the zero value”

Change-Id: I1a302c1e40ca89acbc76897e39097ecd04865460
Reviewed-on: https://go-review.googlesource.com/60290Reviewed-by: Ian Lance Taylor <iant@golang.org>