[tracker] Revert "libtracker-data: Fixes NB#174591, Throw error on undefined variable in expressions"

[Jürg Billeter <juergbi src gnome org>]

commit 49a8f1feeec1569ec35412ea9abf1d61314fee32
Author: Jürg Billeter <j bitron ch>
Date:   Fri Jun 18 11:50:46 2010 +0200

    Revert "libtracker-data: Fixes NB#174591, Throw error on undefined variable in expressions"
    
    This reverts commit ff52af3dc6b72350f08f034d6e4245a6c54221b2.
    
    This broke queries that used SELECT variables in ORDERY BY clauses.

 src/libtracker-data/tracker-sparql-expression.vala |    4 +---
 1 files changed, 1 insertions(+), 3 deletions(-)
---
diff --git a/src/libtracker-data/tracker-sparql-expression.vala b/src/libtracker-data/tracker-sparql-expression.vala
index 60e17de..ea5052f 100644
--- a/src/libtracker-data/tracker-sparql-expression.vala
+++ b/src/libtracker-data/tracker-sparql-expression.vala
@@ -870,9 +870,7 @@ class Tracker.Sparql.Expression : Object {
 			sql.append (variable.sql_expression);
 
 			if (variable.binding == null) {
-				// NB#174591, I replaced `return PropertyType.UNKNOWN` with throw
-				// make-test still works and the query now returns this error.
-				throw get_error ("use of undefined variable `%s'".printf (variable.name));
+				return PropertyType.UNKNOWN;
 			} else {
 				return variable.binding.data_type;
 			}