[BUG] "Wrong type argument: integer-or-marker-p, nil" for C-O outside [[ ]]

[boew]

Issue

Invoking mediawiki-open with cursor NOT between "[[" and "]]" produces
byte-code: Wrong type argument: integer-or-marker-p, nil

WA: (load "boe-mw") with boe-mw.el as below. -- Tested in .emacs after byte-compiling.

Note: Invoking mediawiki-open with cursor between "[[" and "]]" works as expected

boe-mw.el

;;; -*- lexical-binding: t; -*-
(defun mediawiki-drop-from-pipe (s)
  "Return page target, dropping chars from pipe to end
Seems OK also for File: links with attributes"
  (let ((pipepos (seq-position s ?|)))
    (if pipepos
	(substring s 0 pipepos)
      s)))
  
(defun mediawiki-page-at-point ()
  "Return the page name under point.
Typically, this means anything enclosed in [[PAGE]]."
  (let ((pos (point))
         (eol (pos-eol))
         (bol (pos-bol)))
    (save-excursion
      (let* ((start  (when (search-backward "[[" bol t)
                       (+ (point) 2)))
              (end    (when (search-forward "]]" eol t)
                        (- (point) 2)))
              (pagename (mediawiki-drop-from-pipe
			 (when (and
                                (not (eq nil start))
                                (not (eq nil end))
                                (<= pos end)
                                (>= pos start))
                           (buffer-substring-no-properties
                            start end)))))
	(if (and pagename (string= "/"
				   (substring pagename 0 1)))
            (concat mediawiki-page-title pagename))
	pagename))))

(defun mediawiki-open (name)
  "Open a wiki page specified by NAME from the mediawiki engine."
  (interactive
    (let* ((hist (cdr (assoc-string mediawiki-site mediawiki-page-history)))
           (temp-history-symbol (make-symbol "mediawiki-temp-history")))
      (set temp-history-symbol hist)
      (list (read-string "Wiki Page: " (mediawiki-page-at-point) temp-history-symbol))))
  (when (or (not (stringp name))
          (string-equal "" name))
    (error "Need to specify a name"))
  (mediawiki-edit mediawiki-site name))