--- nodequeue.module	2012-09-10 10:35:47.607709564 +0200
+++ nodequeue.module.bak	2012-09-10 10:35:38.859709526 +0200
@@ -405,7 +405,7 @@
  * Implementation of hook_apachesolr_update_index().
  */
 function nodequeue_apachesolr_update_index(&$document, $node) {
-  if (empty($document)) {
+  if (!count((array)$document)) { // ignore empty document objects
     return;
   }