bug#34722: 26.1; REGRESSION: `indent-pp-sexp' Wrong type argument: consp, nil

[Eli Zaretskii]

> Date: Sun, 3 Mar 2019 09:29:32 -0800 (PST)
> From: Drew Adams <drew.adams@oracle.com>
> 
> 1. emacs -Q
> 
> 2. C-x C-f foo.el
> 
> 3. Enter this text. Be sure to hit RET after the final right paren, so there 
> is a newline char at the end.
> 
> (defun foo ()
>   (unless t 42)))
> 
> 
> 4. Put point just before the first left paren, then use `C-M-q'.
> 
> This error is raised:
> 
> Wrong type argument: consp, nil

FWIW, I cannot reproduce this with today's Emacs 27.  Your Emacs 27
build is almost a year old, maybe we had a bug back then.