spec: describe an edge case for slice expression of nil slice
spec: describe an edge case for slice expression of nil slice

Change-Id: I8c0e2b37e7e8cb4db6ad0b456fde7eb908ffbd04
Reviewed-on: https://go-review.googlesource.com/c/go/+/430836
Reviewed-by: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Run-TryBot: Cuong Manh Le <54b4457f1dff6823379654eb5867596497ba782f@gmail.com>
Auto-Submit: Cuong Manh Le <54b4457f1dff6823379654eb5867596497ba782f@gmail.com>
Reviewed-by: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
Auto-Submit: Robert Griesemer <a6752097faebf1f02d80107d77a9be009089afe3@google.com>

golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go,golang/go