log/slog: empty calls to With and WithGroup are no-ops
It doesn't make sense to call Logger.WithGroup with the empty string.
Make it a no-op by returning the receiver.
This relieves handlers of the burden of detecting that case themselves.
Less importantly, but for consistency, if Logger.With is called with
no args, make it a no-op by returning the receiver.
Along the way, fix obsolete mentions of "the Logger's context" in the
doc.
Change-Id: Ia6caa4f1ca70c1c4b0cab3e222b2fda48be73fef
Reviewed-on: https://go-review.googlesource.com/c/go/+/496175
TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Alan Donovan <adonovan@google.com>
Run-TryBot: Jonathan Amsterdam <jba@google.com>