RE: Should nil COLLECTION element mean a "nil" candidate forcompleting-read? Alist doc.

[Drew Adams]

I forgot to point out that treating nil this way can lead to extra (ugly) code,
just to remove or prevent production of such nil entries, so they are not
available to the user.

IOW, I suspect that the number of times where this "feature" might be useful
(for what?) is less than the number of times where it is a nuisance.

A typical case would be mapping a function that can return nil over a list. With
the current behavior, either an extra, nil-removing pass is needed or an
iteration is needed that is a bit more complex (ugly) than a simple mapping.