Something

--- gdk/gdkwindow.c
+++ gdk/gdkwindow.c
@@ -609,18 +609,21 @@ gdk_window_get_parent (GdkWindow *window
 GdkWindow*
 gdk_window_get_toplevel (GdkWindow *window)
 {
   GdkWindowObject *obj;
   
   g_return_val_if_fail (GDK_IS_WINDOW (window), NULL);
 
   obj = (GdkWindowObject *)window;
-  while (GDK_WINDOW_TYPE (obj) == GDK_WINDOW_CHILD)
+  while (obj && GDK_WINDOW_TYPE (obj) == GDK_WINDOW_CHILD) {
     obj = (GdkWindowObject *)obj->parent;
+  }
+
+  g_return_val_if_fail (obj != NULL, NULL);
   
   return GDK_WINDOW (obj);
 }
 
 /**
  * gdk_window_get_children:
  * @window: a #GdkWindow
  * 
@@ -2290,19 +2293,21 @@ gdk_window_update_idle (gpointer data)
   return FALSE;
 }
 
 static gboolean
 gdk_window_is_toplevel_frozen (GdkWindow *window)
 {
   GdkWindowObject *toplevel;
 
+  g_return_val_if_fail (window != NULL, FALSE);
+
   toplevel = (GdkWindowObject *)gdk_window_get_toplevel (window);
 
-  return toplevel->update_and_descendants_freeze_count > 0;
+  return toplevel ? toplevel->update_and_descendants_freeze_count > 0 : FALSE;
 }
 
 static void
 gdk_window_schedule_update (GdkWindow *window)
 {
   if (window &&
       (GDK_WINDOW_OBJECT (window)->update_freeze_count ||
        gdk_window_is_toplevel_frozen (window)))
@@ -2428,16 +2433,19 @@ gdk_window_process_all_updates (void)
   
   update_windows = NULL;
   update_idle = 0;
 
   g_slist_foreach (old_update_windows, (GFunc)g_object_ref, NULL);
   
   while (tmp_list)
     {
+      if(!tmp_list->data)
+        continue;
+
       GdkWindowObject *private = (GdkWindowObject *)tmp_list->data;
       
       if (private->update_freeze_count ||
 	  gdk_window_is_toplevel_frozen (tmp_list->data))
 	update_windows = g_slist_prepend (update_windows, private);
       else
 	gdk_window_process_updates_internal (tmp_list->data);