[tracker] SPARQL: Fix critical when using non-existing resources as objects

[Jürg Billeter <juergbi src gnome org>]

commit 4022c3842e3bc2cbcbd384591ff3ddea221fc36f
Author: Jürg Billeter <j bitron ch>
Date:   Mon May 11 18:29:57 2009 +0200

    SPARQL: Fix critical when using non-existing resources as objects
---
 src/libtracker-data/tracker-sparql-query.vala |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/src/libtracker-data/tracker-sparql-query.vala b/src/libtracker-data/tracker-sparql-query.vala
index 54a05d3..e19eeb0 100644
--- a/src/libtracker-data/tracker-sparql-query.vala
+++ b/src/libtracker-data/tracker-sparql-query.vala
@@ -170,6 +170,9 @@ public class Tracker.SparqlQuery : Object {
 							}
 						}
 					} while (result_set.iter_next ());
+				} else {
+					/* no match */
+					sql.append ("SELECT NULL AS ID, NULL AS \"predicate\", NULL AS \"object\"");
 				}
 			} else if (domain != null) {
 				// any subject, predicates limited to a specific domain