Subject: Re: bug#34852: 26.1; seq-intersection ignores nil as element

From: Stefan Monnier <[email-masked]>
Date: Thu, 14 Mar 2019 09:34:07 -0400

Yet another approach might be to make an exception in seq-contains if
the returned element is nil (and return something else in that case).
E.g.

    diff --git a/lisp/emacs-lisp/seq.el b/lisp/emacs-lisp/seq.el
    index 4a811d7895..d2398eb588 100644
    --- a/lisp/emacs-lisp/seq.el
    +++ b/lisp/emacs-lisp/seq.el
    @@ -360,7 +360,7 @@ seq-sort-by
     Equality is defined by TESTFN if non-nil or by `equal' if nil."
       (seq-some (lambda (e)
                   (when (funcall (or testfn #'equal) elt e)
    -                e))
    +                (or e t)))
                 sequence))
     
     (cl-defgeneric seq-set-equal-p (sequence1 sequence2 &optional testfn)

-- Stefan