--- gvfs-1.4.1.orig/monitor/hal/ghalvolume.c
+++ gvfs-1.4.1/monitor/hal/ghalvolume.c
@@ -778,7 +778,8 @@
                         gpointer user_data)
 {
   ForeignMountOp *data = user_data;
-  data->callback (G_OBJECT (data->enclosing_volume), res, data->user_data);
+  if (data->callback)
+    data->callback (G_OBJECT (data->enclosing_volume), res, data->user_data);
   g_object_unref (data->enclosing_volume);
   g_free (data);
 }
--- gvfs-1.4.1.orig/monitor/proxy/gproxyvolume.c
+++ gvfs-1.4.1/monitor/proxy/gproxyvolume.c
@@ -778,7 +778,8 @@
                         gpointer user_data)
 {
   ForeignMountOp *data = user_data;
-  data->callback (G_OBJECT (data->enclosing_volume), res, data->user_data);
+  if (data->callback)
+    data->callback (G_OBJECT (data->enclosing_volume), res, data->user_data);
   g_object_unref (data->enclosing_volume);
   g_free (data);
 }
