bug#67587: 30.0.50; function defined by cl-defmethod returns nil instead of fixed str

[Vonfry]

    (cl-defmethod foo ((_e (eql foo))) "docstr" "result str")
    (foo 'foo)

    In Emacs 29, it returns "result str", but nil in Emacs 30.


In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo
version 1.18.0, Xaw3d scroll bars)
Repository revision: eec1142acdde9d10781c781e7890c2d26f7e6b2d
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12101009
System Description: NixOS 24.05 (Uakari)

Configured using:
 'configure
 --prefix=/nix/store/fhijpc8iazd3xn9881mfwfwjs63bfwdf-emacs-git-20231201.0
 --disable-build-details --with-modules --with-x-toolkit=lucid
 --with-xft --with-cairo --with-native-compilation --with-tree-sitter'

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GPM GSETTINGS HARFBUZZ JPEG JSON
LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 M17N_FLT MODULES NATIVE_COMP NOTIFY
INOTIFY PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS TREE_SITTER WEBP X11 XAW3D XDBE XIM XPM LUCID ZLIB

Important settings:
  value of $EMACSLOADPATH: 
  value of $EMACSNATIVELOADPATH: 
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=fcitx
  locale-coding-system: utf-8-unix