A lot of upower clients expect to get some answer from up_client_get_devices().
So to avoid fixing all consumers we want to return empty device list to them.

--- upower-0.99.11/libupower-glib/up-client.c	2019-07-07 10:29:27.000000000 +0000
+++ upower-0.99.11/libupower-glib/up-client.c	2020-01-05 11:05:13.731804295 +0000
@@ -115,17 +115,17 @@ up_client_get_devices2 (UpClient *client
 
 	g_return_val_if_fail (UP_IS_CLIENT (client), NULL);
 
+	array = g_ptr_array_new_with_free_func ((GDestroyNotify) g_object_unref);
+
 	if (up_exported_daemon_call_enumerate_devices_sync (client->priv->proxy,
 							    &devices,
 							    NULL,
 							    &error) == FALSE) {
 		g_warning ("up_client_get_devices failed: %s", error->message);
 		g_error_free (error);
-		return NULL;
+		return array;
 	}
 
-	array = g_ptr_array_new_with_free_func ((GDestroyNotify) g_object_unref);
-
 	for (i = 0; devices[i] != NULL; i++) {
 		UpDevice *device;
 		const char *object_path = devices[i];