Bug 18936: (follow-up) fix rental discount lookup

Signed-off-by: Minna Kivinen <minna.kivinen@hamk.fi>
Signed-off-by: Joonas Kylmälä <joonas.kylmala@helsinki.fi>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>

C4/Circulation.pm

@@ -3283,19 +3283,19 @@ sub _get_discount_from_rule {
             categorycode => $categorycode,
         },
         {
-            branchcode   => '*',
+            branchcode   => undef,
             categorycode => $categorycode,
             itemtype     => $itemtype,
         },
         {
             branchcode   => $branchcode,
             categorycode => $categorycode,
-            itemtype     => '*',
+            itemtype     => undef,
         },
         {
-            branchcode   => '*',
+            branchcode   => undef,
             categorycode => $categorycode,
-            itemtype     => '*',
+            itemtype     => undef,
         },
     );