Re: (symbol-plist nil) => not empty

[Richard Stallman]

    (custom-group 
     ((nntp-authinfo-file custom-variable)
      (ada-tight-gvd-integration custom-variable)
      (breakpoint-enabled-bitmap-face custom-face)
      (breakpoint-disabled-bitmap-face custom-face)
      (nnimap-authinfo-file custom-variable)
      (nnimap-prune-cache custom-variable)
      (vc-arch-mode-line-rewrite custom-variable))

     event-symbol-element-mask (nil 0)

     event-symbol-elements (nil)

     modifier-cache ((0))

     custom-loads (ada-xref gdb-ui nnimap nntp vc-arch))

    The customize things are variables and faces which
    are lacking a :group specification.

Would you like to give them :group specifications?

As for event-symbol-elements, it looks like something in C
called parse_modifiers on Qnil.  That could be a bug.
It happens after the dumped Emacs is run.
With a conditional breakpoint, you could find out why.