[grilo] core: check for 'key-depends' implementation

[Victor Manuel Jaquez Leal <vjaquez src gnome org>]

commit 5ae56cab0c71f9b1964260e424214fab219d230f
Author: Simón Pena <spenap gmail com>
Date:   Thu Sep 9 22:08:58 2010 +0200

    core: check for 'key-depends' implementation

 src/grl-metadata-source.c |    7 ++++++-
 1 files changed, 6 insertions(+), 1 deletions(-)
---
diff --git a/src/grl-metadata-source.c b/src/grl-metadata-source.c
index 4ec06ff..81817bf 100644
--- a/src/grl-metadata-source.c
+++ b/src/grl-metadata-source.c
@@ -548,7 +548,12 @@ const GList *
 grl_metadata_source_key_depends (GrlMetadataSource *source, GrlKeyID key_id)
 {
   g_return_val_if_fail (GRL_IS_METADATA_SOURCE (source), NULL);
-  return GRL_METADATA_SOURCE_GET_CLASS (source)->key_depends (source, key_id);
+
+  if (GRL_METADATA_SOURCE_GET_CLASS (source)->key_depends) {
+    return GRL_METADATA_SOURCE_GET_CLASS (source)->key_depends (source, key_id);
+  } else {
+    return NULL;
+  }
 }
 
 /**