bug#34996: 27.0.50; gnus-group-read-ephemeral-group is broken

[Alex Branham]

Try for example M-x gnus-read-ephemeral-emacs-bug-group RET 34671 RET.
For me, it triggers this backtrace:

Debugger entered--Lisp error: (wrong-type-argument hash-table-p nil)
  (puthash "nndoc+ephemeral:bug#34671" nil nil)
  (gnus-group-read-ephemeral-group "nndoc+ephemeral:bug#34671" (nndoc 
"/tmp/gnus-temp-group-Zb681Z" (nndoc-article-type mbox)) nil nil)
  (gnus-read-ephemeral-bug-group (34671) 
"https://debbugs.gnu.org/cgi/bugreport.cgi?bug=%s;m..."; nil)
  (gnus-read-ephemeral-emacs-bug-group 34671)
  (funcall-interactively gnus-read-ephemeral-emacs-bug-group 34671)
  (call-interactively gnus-read-ephemeral-emacs-bug-group record nil)
  (command-execute gnus-read-ephemeral-emacs-bug-group record)

In GNU Emacs 27.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.5)
 of 2019-03-25 built on localhost
Windowing system distributor 'The X.Org Foundation', version 11.0.11906000
System Description: NixOS 18.09.2375.680f9d7ea90 (Jellyfish)

Configured using:
 'configure
 --prefix=/nix/store/f7lyihh5mid6rv73xdvz30ssmf4mnzya-emacs-27.0.50
 --with-modules --with-x-toolkit=gtk3 --with-xft
 CFLAGS=-DMAC_OS_X_VERSION_MAX_ALLOWED=101200'

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND DBUS GSETTINGS GLIB NOTIFY INOTIFY
LIBSELINUX GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD JSON
PDUMPER GMP

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix