Using Org protocol capture without supplying a URL inserts a corrupt entry into org-stored-links (nil ""). The nil causes a type error later in org-insert-link.
(defun org-protocol-do-capture (info) "Perform the actual capture based on INFO." (let* ((temp-parts (org-protocol-parse-parameters info)) (parts (cond ((and (listp info) (symbolp (car info))) info) ((= (length (car temp-parts)) 1) ;; First parameter is exactly one character long (org-protocol-assign-parameters temp-parts '(:template :url :title :body))) (t (org-protocol-assign-parameters temp-parts '(:url :title :body))))) (template (or (plist-get parts :template) org-protocol-default-template-key)) (url (and (plist-get parts :url) (org-protocol-sanitize-uri (plist-get parts :url)))) (type (and url (string-match "^\\([a-z]+\\):" url) (match-string 1 url))) (title (or (plist-get parts :title) "")) (region (or (plist-get parts :body) "")) (orglink (if url (org-make-link-string url (if (string-match "[^[:space:]]" title) title url)) title)) (org-capture-link-is-already-stored t)) ;; avoid call to org-store-link (setq org-stored-links (cons (list url title) org-stored-links)) Emacs : GNU Emacs 26.1 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.22.30) of 2018-07-05 Package: Org mode version 9.1.14 (9.1.14-1059-gadec50-elpaplus @ /home/ionasal/.emacs.d/elpa/org-plus-contrib-20181211/)