Index: privatemsg.module
===================================================================
RCS file: /cvs/drupal/contributions/modules/privatemsg/privatemsg.module,v
retrieving revision 1.70.2.30.2.91.2.78
diff -u -p -r1.70.2.30.2.91.2.78 privatemsg.module
--- privatemsg.module	19 Oct 2009 00:00:59 -0000	1.70.2.30.2.91.2.78
+++ privatemsg.module	19 Oct 2009 21:15:59 -0000
@@ -1476,7 +1476,7 @@ function privatemsg_new_thread($recipien
  *
  * @ingroup api
  */
-function privatemsg_reply($thread_id, $body = NULL, $options = array()) {
+function privatemsg_reply($thread_id, $body, $options = array()) {
   global $user;
   $author = drupal_clone($user);
 
@@ -1541,6 +1541,16 @@ function _privatemsg_validate_message(&$
     }
   }
 
+  // Don't allow replies without a body.
+  if (!empty($message['thread_id']) && empty($message['body'])) {
+    if ($form) {
+      form_set_error('body', t('Disallowed to send reply without a message.'));
+    }
+    else {
+      $messages['error'][] = t('Disallowed to send reply without a message.');
+    }
+  }
+
   if (empty($message['recipients']) || !is_array($message['recipients'])) {
     if ($form) {
       form_set_error('to', t('Disallowed to send a message without atleast one valid recipient'));