(bibtex-autokey-before-presentation-function): Fix :type.

diff --git a/lisp/textmodes/bibtex.el b/lisp/textmodes/bibtex.el
index 37e5152be83c3ca6d288be634d034e43659b1f3c..a7c68a72040cb6b0615bde4aad230d854ac476c8 100644 (file)
--- a/lisp/textmodes/bibtex.el
+++ b/lisp/textmodes/bibtex.el
@@ -685,7 +685,7 @@ the generated key is presented (in entry or, if
 must take one argument (the automatically generated key), and must
 return with a string (the key to use)."
   :group 'bibtex-autokey
-  :type 'function)
+  :type '(choice (const nil) function))
 
 (defcustom bibtex-entry-offset 0
   "*Offset for BibTeX entries.