Hi Glenn,

The nil is useful for distinguish default value from custom setting value.

What’s the lisp for your testing? Could you share them?

From: Glenn Morris
Sent: Wednesday, May 19, 2021 23:48
To: Lars Ingebrigtsen
Cc: 47119@debbugs.gnu.org; Sun Lin; Eli Zaretskii; Lin Sun
Subject: Re: bug#47119: 28.0.50; [patch][Dired] new user option for compressing dir suffix

I also wonder how useful it is to say eg "the default nil means .tar"

rather than just making the default value be ".tar"?

(Spotted because the custom :type did not allow for nil.)