unity_scope_dbus_connector_export() reports obscure error message

[Shuduo Sang]

OS: ubuntu 13.10 saucy
libunity: 7.1.2+13.10.20131010-0ubuntu2

when I call unity_scope_dbus_connector_export() with an illegal dbus name like "com.canonical.Unity.Scope.Graphics.500px", the error message is obscure to understand

204 connector = unity_scope_dbus_connector_new(UNITY_ABSTRACT_SCOPE(scope));
(gdb)
205 assert(connector);
(gdb)
207 unity_scope_dbus_connector_export(connector, NULL);
(gdb)
[New Thread 0x7fffef0f7700 (LWP 7997)]
208 unity_scope_dbus_connector_run();
(gdb)

(process:7988): GLib-GIO-CRITICAL **: g_bus_own_name: assertion 'g_dbus_is_name (name) && !g_dbus_is_unique_name (name)' failed