Max Nikulin <manikulin@gmail.com> writes:

> Trying to export (to HTML buffer)
>
>      src_elisp[:exports source]{a}
>
> I have got an obscure error
>
>      org-export-as: Wrong type argument: char-or-string-p, nil
>
> I believe, some meaningful error should be signaled.
>
> I was quite surprised since the following is exported with no error
>
>      #+begin_src elisp :exports source
>        a
>      #+end_src

Confirmed.

The behavior on unknown value of :exports header arg is undefined.
We may, however, show a warning in such scenario and avoid throwing
cryptic error.
See the attached tentative patch.