bug#48479: 28.0.50; Crash on `read--expression'

[Eli Zaretskii]

> From: Mattias Engdegård <mattiase@acm.org>
> Date: Mon, 17 May 2021 22:01:10 +0200
> Cc: 48479@debbugs.gnu.org
> 
> 17 maj 2021 kl. 17.14 skrev Eli Zaretskii <eliz@gnu.org>:
> 
> > Thanks, this was caused by a recent addition of the :success handler.
> > I tried to fix that on the master branch now.
> 
> Thank you for fixing that, and sorry about the oversight.

No sweat.

> It prompts the question why we are so permissive in the first place -- a nil 
> handler is malformed and always a mistake. Raising an error is probably more 
> helpful. Although someone may be relying on this undocumented behaviour it 
> sounds unlikely. Given that it has elicited a byte-compiler warning for a 
> very long time (probably something like 17 years), we ought to be forgiven 
> for turning it into an error now, wouldn't we?

What would be the advantage of making it an error?