Specify the behavior of hierarchical-list-compound-item<%>:open if its parent is not open

Version

Racket 7.4 on Debian 9.

How to reproduce

Save this in hierlist-error.rkt:

#lang racket/base

;;  hierlist-error.rkt

(require
    racket/class
    racket/gui/base
    mrlib/hierlist
)

(provide
    main
)

(define (main)
    (define frame (new frame% [label "hierlist-error.rkt"] [width 800] [height 600]))
    (define hlist (new hierarchical-list% [parent frame]))
    (define hcompound-1 (send hlist new-list))
    (define hcompound-1-1 (send hcompound-1 new-list))
    ;;  This throws an exception.
    (send hcompound-1-1 open)
    (send frame show #t)
)

Then, run:

racket -t hierlist-error.rkt -m

We get this NullPointerException:

end: target is not an object
  target: #f
  method name: get-text-extent
  context...:
   racket-7.4/share/pkgs/gui-lib/mrlib/arrow-toggle-snip.rkt:161:4: set-state method in arrow-toggle-snip%
   racket-7.4/share/pkgs/gui-lib/mrlib/hierlist/hierlist-unit.rkt:479:13: handle-open method in hierarchical-list-snip%

Expected behavior

I expect hcompound-1-1 to change its internal state to open, so that when its parent is opened, it will be open by default.

Reproduce the failure with racket -t hierlist-error.rkt -m, then inspect arrow-toggle-snip.rkt and hierlist-unit.rkt at the stack-trace locations. Confirm the intended state transition for opening a child whose parent is closed, and verify that opening the parent later reflects that state without raising the reported exception.