bug#31718: 26.1; Strange behavior of `cond'

[Drew Adams]

> You're right, my mistake. Still, I prefer using (cons nil nil) since it's
> cheaper and is a common way to address this issue elsewhere.

Both ways are traditional, the cons-cell one being probably
more typical (and so more recognizable).

In any case, for such a (good, not bad) hack - either one,
a comment is always in order, I think.