org-map-entries says "Wrong type argument: char-or-string-p, nil"

Question

I have this code:

(defun org-get-logbook-notes ()
  (save-excursion
    (unless (org-at-heading-p)
      (outline-previous-heading))
    (when (re-search-forward ":LOGBOOK:" (save-excursion
                                           (outline-next-heading)
                                           (point))
                             t)
      (let* ((elt (org-element-property-drawer-parser nil))
             (beg (org-element-property :contents-begin elt))
             (end (org-element-property :contents-end elt)))
        (buffer-substring-no-properties beg end)))))

(require 's)

(defun my/org-rotten-set ()
(interactive "P")
(setq lognotes (org-get-logbook-notes))
(setq numresched (number-to-string (s-count-matches "Rescheduled from" lognotes))) 
(org-entry-put nil "ROTTEN" numresched ))

What it should do is simply the following task:

• Get the contents of the :LOGBOOK: drawer
• Count how many times the string "Rescheduled from" occurs
• Transform this into a number and create a property "ROTTEN" with this number as a value

If I use IELM, place the point inside a single entry in my orgfile and execute

ELISP> (my/org-rotten-set)

This works perfectly fine. The occurences of "Rescheduled from" will be count, the "ROTTEN" property will be created.

Now if I try to use this function together with org-map-entries it doesn't work.

ELISP> (org-map-entries 'my/org-rotten-set)
*** Eval error ***  Wrong type argument: char-or-string-p, nil

What am I doing wrong here? It seems to be related to the org-get-logbook-notes function that I defined a the beginning, but I have no idea why?

Answer 1

org-map-entries operates on whatever you specify as its SCOPE (see the doc string for details). Since you have not expicitly specified the scope in your call, it is nil: that means it operates on the current buffer (respecting the restriction, if any - but that's unimportant here). The main point is that you are executing it in the IELM buffer, so that's the current buffer, not your Org mode file.

Try

(with-current-buffer (get-buffer "name of your Org mode file here")
   (org-map-entries #'my/org-rotten-set))

But there is a problem in my/org-rotten-set that you need to fix: if there is no LOGBOOK drawer in an entry, (org-get-logbook-notes) will return nil and that will cause s-count-matches to give you the error you get: " (wrong-type-argument char-or-string-p nil)". You need to check the return value and do nothing if it is nil:

(defun my/org-rotten-set ()
  (interactive)
  (setq lognotes (org-get-logbook-notes))
  (when lognotes
    (setq numresched (number-to-string (s-count-matches "Rescheduled from" lognotes))) 
    (org-entry-put nil "ROTTEN" numresched )))

It's also better to use let-bound variables in the function, rather than using setq and global variables :

(defun my/org-rotten-set ()
  (interactive)
  (let ((lognotes (org-get-logbook-notes)))
    (when lognotes
      (org-entry-put nil "ROTTEN" (number-to-string 
                                    (s-count-matches "Rescheduled from" lognotes))))))

Another (less likely) problem is that if the string ":LOGBOOK:" occurs in the file (outside the context of a LOGBOOK drawer), org-get-logbook-entries might get confused. I'll leave that problem for the interested reader to pursue :-)