>>>>> On Mon, 30 Sep 2019 17:45:39 +0200, Lars Ingebrigtsen <larsi@gnus.org> said:

    Lars> Robert Pluim <rpluim@gmail.com> writes:
    >> (defcustom winner-boring-buffers-regexp nil
    >> "`winner-undo' will not restore windows with buffers matching this regexp."
    >> -  :type 'string
    >> +  :type '(choice (string :tag "Regexp")
    >> +                 (const :tag "Don't check" nil))
    >> :version "27.1")
    >> 
    >> Iʼm not sure those are worth fixing.

    Lars> I think fixing those would be a win.

Hmm. Current attempt attached. Iʼm having trouble with
'sql-postgres-login-params', and 'sql-password-wallet', probably
because I donʼt know enough about custom, suggestions welcome.

    >> I did spot what seem to be some genuine errors though (hmm, would
    >> flymake-cc-command need a :version tag update as well? The existing
    >> definition makes customize error out)

    Lars> [...]

    >> -  :type 'bool
    >> +  :type 'boolean

    Lars> etc.  Looks good to me; please push.

Done. One more, which I missed because itʼs not defined from lisp. Iʼm
not so sure about mentioning U+2502 in the tag, since I have a
vague memory that nil actually means 'autodetect if the frame can
display U+2502'.

diff --git a/lisp/cus-start.el b/lisp/cus-start.el
index 15d33b43c0..6b8fa0c6c9 100644
--- a/lisp/cus-start.el
+++ b/lisp/cus-start.el
@@ -671,9 +671,11 @@ minibuffer-prompt-properties--setter
               :safe (lambda (value) (or (booleanp value) (integerp value))))
              (display-fill-column-indicator-character
               display-fill-column-indicator
-              character
+              (choice
+               (const :tag "Default (U+2502)" nil)
+               (character :tag "Character" ))
               "27.1"
-              :safe characterp)
+              :safe (lambda (value) (or (characterp value) (null value))))
 	     ;; xfaces.c
 	     (scalable-fonts-allowed display boolean "22.1")
 	     ;; xfns.c