[bug-report] potential bug of emms-playlist-mode on Emacs 27.1

[John Wong]

Hi EMMS Team,

I have been enjoying emms with emacs - the best way to enjoy music and
podcasts while doing my stuff in emacs.

Yesterday after I upgraded my system to Devuan Chimaera (a systemd
free, SysVinit version of Debian Bulleye) and hence the distributed
Emacs to 27.1, the emms-playlist-mode doesn't work like before:
1. I can still connect to mpd using emms-player-mpd-connect
2. I can get to the mpd playlist using emms-playlist-mode-go
3. I can even play music using emms-player-mpd-play

But whenever I interact with mpd using the emms-playlist-mode
functions, or interact with mpd using the emacs *EMMS Playlist* buffer
(e.g. press enter to play the song at the current line), the following
happens:
1. an error message appears at the mini-buffer as follow:-
error in process filter: Spurious communication from process mpd, see
buffer *spurious*
2. the "playing", i.e. no playing but error message and proceeding to
the next song on the playlist, keeps on going until the end of the
playlist. And then another message in mini-buffer appears:-
No next track in playlist
3. The *spurious* buffer has just the following followed by a newline
OK MPD 0.22.4

I am not sure if it is me or if it is some incompatibility issues with
Emacs 27.1. Here are the details of my settings:
MPD version 0.22.6
GNU Emacs 27.1 "(build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.24,
cairo version 1.16.0) of 2021-03-28, modified by Debian"
EMMS 20211211.232 from MELPA

Thanks for all the effort and generosity on this EMMS project and the
maintenance. I wish all of you a nice Christmas time and a good new
year 2022 to come!

Best,
John Wong