Eli Zaretskii <eliz@gnu.org> writes:

>> +               (and bx (or (not lh) (> (if (listp lh) (cdr lh) lh) 0))))
>                                                ^^^^^
> Shouldn't that be 'consp' instead?  'listp' returns non-nil for nil
> argument.

I’m not expert enough to say more than that either way works to fix the
issue. Originally I did the ‘(cdr lh)’ unconditionally and got an error
mentioning ‘listp’ so I just used that when I added the condition; if it
had said ‘conps’ I would have used that.

Here is the patch with ‘consp’ instead.