[rygel] media-export: Fix crash on single-level query containers

[Zeeshan Ali Khattak <zeeshanak src gnome org>]

commit 39fe9b707453599c5ca7d48b3ab4a3b97f797580
Author: Jens Georg <mail jensge org>
Date:   Fri Mar 5 19:16:26 2010 +0100

    media-export: Fix crash on single-level query containers

 src/rygel/rygel-media-db.vala |    8 ++++----
 1 files changed, 4 insertions(+), 4 deletions(-)
---
diff --git a/src/rygel/rygel-media-db.vala b/src/rygel/rygel-media-db.vala
index 6760f03..348e398 100644
--- a/src/rygel/rygel-media-db.vala
+++ b/src/rygel/rygel-media-db.vala
@@ -929,10 +929,10 @@ public class Rygel.MediaDB : Object {
     }
 
     public Gee.List<string> get_object_attribute_by_search_expression (
-                                       string           attribute,
-                                       SearchExpression expression,
-                                       long             offset,
-                                       long             max_count) throws Error {
+                                       string            attribute,
+                                       SearchExpression? expression,
+                                       long              offset,
+                                       long              max_count) throws Error {
         var args = new ValueArray (0);
         var filter = this.search_expression_to_sql (expression, args);
         if (filter != null) {