--- nodequeue.module
+++ nodequeue.module
@@ -1993,6 +1994,8 @@ function nodequeue_remove_subqueue($sqid) {
  *   The node ID
  */
 function nodequeue_subqueue_add($queue, &$subqueue, $nid) {
+  // make sure to only do sth if a valid node is given
+	if (!empty($nid)) {
   // If adding this would make the queue too big, pop the front node
   // (or nodes) out.
 
@@ -2009,6 +2012,7 @@ function nodequeue_subqueue_add($queue, &$subqueue, $nid) {
 
   // Invoke the hook to notify other modules of the node addition.
   module_invoke_all('nodequeue_add', $subqueue->sqid, $nid);
+	}
 }
 
 /**