bug#37256: 27.0.50; Error (wrong-type-argument stringp nil) thrown when calling (load-theme 'solarized-dark t)

[Eli Zaretskii]

> From: Benjamin Orthen <benjamin@orthen.net>
> Date: Sun, 1 Sep 2019 17:07:14 +0200
> 
> 1. Call emacs -Q
> 2. Call "M-x load-theme" interactively
> 3. Error is thrown: (wrong-type-argument stringp nil)
> 4. Same happens with (load-theme '<some-theme> t) or "M-x
> customize-themes"
> Did not have this error 3 weeks ago when I last built emacs from source.
> 
> 5. With debug-init and loading my init file, the backtrace looks as
> follows:
> 
> Debugger entered--Lisp error: (wrong-type-argument stringp nil)
>   file-directory-p(nil)
>   custom-theme--load-path()

Paul, I think this is because user-emacs-directory is now nil
initially.  custom-theme-directory then is computed as nil, and
custom-theme--load-path isn't ready for that.