Index: book.admin.inc
===================================================================
RCS file: /cvs/drupal/drupal/modules/book/book.admin.inc,v
retrieving revision 1.12
diff -u -r1.12 book.admin.inc
--- book.admin.inc	5 Jul 2008 06:00:51 -0000	1.12
+++ book.admin.inc	8 Oct 2008 13:38:33 -0000
@@ -109,6 +109,11 @@
   $order = array_flip(array_keys($form['#post']['table']));
   $form['table'] = array_merge($order, $form['table']);
 
+  if (empty($form['#post']['table'])) {
+    drupal_set_message(t('Nothing to update in book %title.', array('%title' => $form['#node']->title)));
+    return;
+  }
+
   foreach (element_children($form['table']) as $key) {
     if ($form['table'][$key]['#item']) {
       $row = $form['table'][$key];