Lexical-let error about ert-runner.el HOT 7 CLOSED

(ert-deftest test-dionysos-process-can-start-process ()
  :tags '(process current)
  (with-test-sandbox
   (with-music-file
    "resources/Roulement_tambour-01.mp3"
    (dionysos--create-process
     dionysos--process-name "mpg123" (list file) (lambda () (message "ok")))
    (should (equal 'run (dionysos--status-process dionysos--process-name)))
    (dionysos--kill-process dionysos--process-name)
    (should (equal nil (process-list))))))

(defun dionysos--create-process (process-name command arguments &optional hook)
  "Create a new asynchronous process.
`PROCESS-NAME' is used to identify this process
`COMMAND' correspond to the program running
`ARGUMENTS' are arguments passed to the program.
`HOOK' is called when process is finished."
  (message "[dionysos-process] Create %s %s %s %s"
           process-name command arguments hook)
  (let ((status (dionysos--status-process process-name)))
    (message "[dionysos-process] Status : %s" status)
    (unless (equal 'run status)
      (lexical-let ((hook hook))
        (let ((process (apply 'start-process process-name nil command arguments)))
          (set-process-sentinel
           process
           (lambda (process event)
             (dionysos--process-sentinel process event hook))))))))