Please ignore that.. that bug is there but has nothing to do with your
recent commit.
I see it on emacs 25.1 RC2 too when I end up causing a timer error in
pdf-tools package:

=====
Interleave enabled
doc-view-goto-page: Wrong type argument: stringp, nil
Error running timer ‘pdf-cache--prefetch-start’: (error "epdfinfo: No such
page 0")
=====



On Mon, Aug 22, 2016 at 9:03 AM Kaushal Modi <kaushal.modi@gmail.com> wrote:

> Actually, it seems like one of the existing windows gets cloned and that
> is put on top of the minibuffer without modeline.
>
> It looks something like this.
>
> So the minibuffer looks completely fused with Win 2 of Buf x (that somehow
> got created automatically when I enabled debug-on-error).
> After some window switching, the mode line for Win 2 appears automatically.
>
> ==============================================
> | Win 1 - Buf x                              |
> ----------------------------------------------
> | Mode-line for Win 1                        |
> ==============================================
> | Win 2 - Buf x                              |
> ----------------------------------------------
> | Minibuffer                                 |
> ==============================================
>
-- 

Kaushal Modi