Hi,

I have the org-html-postamble-format set to the below:

(setq org-html-postamble-format
                  `(("en"
                     ,(concat "Exported using "
                              ;; "%c" is replaced with
`org-html-creator-string'
                              ;; Emacs <VERSION> (Org mode <VERSION>)
                              "<div style=\"display: inline\"
class=\"creator\">"
                              "%c</div> "
                              "by %a. — "
                              "<div style=\"display: inline\"
class=\"date\">"
                              "%d</div>"))))


It works great except for the cases where I have set a document author to
nothing using

#+AUTHOR:

What would be the best way to set the postamble so that the "by %a" portion
does not get printed if the %a value is "".

Right now, if the author is nil, the postamble gets exported as:

Exported using
Emacs <http://www.gnu.org/software/emacs/> 25.0.50.1 (Org
<http://orgmode.org/> mode 8.3.3)
 by . —
Jan 26 2016, Tue