title: orgmode emacs cannot export to html
body: <p>When I evaluate a code block (see example below), it works. However; when I tried to export to html I got the next error:
  <strong>Wrong type argument: stringp, nil</strong></p>
  
  <p>If I take the <em>C</em> from   -- #+begin_src C -- , it will export without any problem. How I can solve the problem?</p>
  
  <p>Thanks</p>
  
  <pre><code>#+begin_src C  :includes &lt;stdio.h&gt; :exports both
  int main(void){
  printf("hello world");
  return 0;
  }
  #+end_src
  
  #+results:
  : hello world
  </code></pre>