bug#48408: BUGFIX: window-default-font-height: check for nil string

[Boruch Baum <boruch_baum@gmx.com>]

On 2021-05-16 08:25, Eli Zaretskii wrote:
> > Date: Sun, 16 May 2021 00:42:15 -0400
> > From: Boruch Baum <boruch_baum@gmx.com>
> > Cc: 48408@debbugs.gnu.org
> >
> > On 2021-05-16 07:22, Eli Zaretskii wrote:
> > >   (terminal-live-p ":0.0")
> >
> > on tty frame: nil
> > on gui frame: nil
> >
> > >   (framep ":0.0")
> >
> > on tty frame: nil
> > on gui frame: nil
> >
> > >   (frames-on-display-list ":0.0")
> >
> > on tty frame: (#<frame F152 0x5599a3b27720>)
> > on gui frame: (#<frame F152 0x5599a3b27720>)
>
> Thanks.  So you have just one frame in that session, which is a TTY
> frame?  I thought it was a session with both GUI and TTY frames, is
> that not so?

I have several frames: at least one is definitely a gui frame (ie. it
appears in its own gui 'window' after being created via a gui menu which
seems to have accessed a gui emacsclient.desktop file), and at least one
is definitely a tty frame (ie. my original 'emacs -nw' invocation, from
within tmux).

In performing the final test again:

> > >   (frames-on-display-list ":0.0")

on tty frame: (#<frame F153 0x5599a3a9d710>)
on gui frame: (#<frame F153 0x5599a3a9d710>)

So the output remains the same, but what you didn't ask me to report was
the mode line output, which differs:

on tty frame: -UUU:@**--F139  *Ibuffer*
on gui frame: -UUU:@**--      *Scratch*

Yes, the mode line displays a frame ID different than the
frames-on-display-list output.

Frame 153 does exist: It is the frame created by my email client (mutt)
to compose this email message). So, it would be the most recent tty
frame created, although the GUI frame was created after.

Changing buffers on either frame does not alter the mode-line output for
frame.

Performing 'C-x 5 b' (M-x select-frame-by-name) on either gui or the
non-mutt tty frame only offers one completion candidate option: F139.
The mutt tty frame offers the single completion candidate F153.

Manually create a second frame on the non-mutt tty (C-x 5 2, C-x 5 ,foo).

Perform M-x select-frame-by-name again, and on the non-mutt tty frame
get two completion options: F139 and foo. On the mutt tty frame, just
F153. On the GUI frame, although the mode line hasn't changed, the only
completion candidate is 'emacs@E15' (E15 being the device hostname).
This completion candidate never appears in the tty frame.

> Anyway, the above probably means we set up frame parameters
> incorrectly somewhere.  Hmm...

Can you reproduce this?

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