We could put in a 'return null' string there, but that is the default 
return value if no return() statement is present, which is perfectly 
valid (return() is optional - see 
http://www.php.net/manual/en/functions.returning-values.php).



the multipart/mixed viewer is not supposed to return any rendered text 
since it is a container class only.

this is the code in the imp/lib/MIME/Viewer/multipart.php:



   /**

      * Render out the currently set contents.

      *

      * @access public

      *

      * @param array $params  An array with a reference to a MIME_Contents

      *                       object.

      *

      * @return string  The rendered text in HTML.

      */

     function render($params)

     {

         $contents = &$params[0];



         foreach ($this->mime_part->getParts() as $part) {

           $contents->buildMessagePart($part);



         }



     }



notice the missing return statement. how could this work? I've checked 
and the caller actually uses the returned value as if it was actually 
a string