Submenu with easy-menu-define yielding invalid menu item

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I am making menus with "easy-menu-define". But I am having difficulty calling the submenu "dingo-outline-subm"
from "easy-menu-define". Would appreciate some assistance figuring out the problem.

The error captured is

Lisp error: (error "Invalid menu item in easymenu")

---------------------

;; Make submenu outline

(defvar dingo-outline-subm

'("Outline"

["Hide Direct Body" outline-hide-entry :help "Hide Entry"]

["Expose Direct Body" outline-show-entry :help "Show Entry"]

["Expose Headings" outline-hide-body :help "Hide Body"])

"Submenu giving outline capability.")

;; Make top menu dingo

(defun dingo-easym ()

"Dingo easy menu."

(easy-menu-define dingo-menu global-map "Dingo"

'("Dingo"

dingo-outline-subm

["Hide Entry" outline-hide-entry t]

["Show Entry" outline-show-entry t]

["Hide Body" outline-hide-body t])) )