wrong-type-argument symbolp "^\\*Ilist\\*$"

Version: 9361aa4d
Emacs: GNU Emacs 27.0.91

I'm trying to use this example from the readme:

(use-package dbc
  :config
  (dbc-add-ruleset "right" '(dbc-actions-right) 300)
  (dbc-add-rule "right" "help" :newname "\\*help\\*"))

I'm getting this error:

Debugger entered--Lisp error: (wrong-type-argument symbolp "^\\*Ilist\\*$")
  symbol-name("^\\*Ilist\\*$")
  dbc-switch-function-get-priority("^\\*Ilist\\*$")
  #f(compiled-function (x) #<bytecode 0x1569e3af423d>)(("^\\*Ilist\\*$" imenu-list-display-buffer))
  #f(compiled-function (cl-x cl-y) #<bytecode 0x1569e41ff351>)((dbc-switch-function-right-300 dbc-actions-right) ("^\\*Ilist\\*$" imenu-list-display-buffer))
  sort((("^\\*Ilist\\*$" imenu-list-display-buffer)) #f(compiled-function (cl-x cl-y) #<bytecode 0x1569e41ff351>))
  cl-sort((("^\\*Ilist\\*$" imenu-list-display-buffer)) < :key #f(compiled-function (x) #<bytecode 0x1569e3af423d>))
  dbc-add-ruleset("right" (dbc-actions-right) 300)
  (progn (dbc-add-ruleset "right" '(dbc-actions-right) 300))
  eval((progn (dbc-add-ruleset "right" '(dbc-actions-right) 300)) t)
  elisp--eval-last-sexp(nil)
  eval-last-sexp(nil)
  funcall-interactively(eval-last-sexp nil)
  call-interactively(eval-last-sexp nil nil)
  command-execute(eval-last-sexp)