[gtk+] reftests: Use $(NULL) in the Makefile

[Benjamin Otte <otte src gnome org>]

commit dc216cf53758dbb1a92d15296dbd51f185bf439b
Author: Colin Walters <walters verbum org>
Date:   Tue May 7 14:48:36 2013 +0200

    reftests: Use $(NULL) in the Makefile

 tests/reftests/Makefile.am |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)
---
diff --git a/tests/reftests/Makefile.am b/tests/reftests/Makefile.am
index 3d8b3b6..e5d9d03 100644
--- a/tests/reftests/Makefile.am
+++ b/tests/reftests/Makefile.am
@@ -1,4 +1,5 @@
 include $(top_srcdir)/Makefile.decl
+NULL =
 
 TEST_PROGS += gtk-reftest
 
@@ -272,6 +273,7 @@ EXTRA_DIST += \
        unresolvable.ref.ui \
        unresolvable.ui \
        window-default-size.ref.ui \
-       window-default-size.ui
+       window-default-size.ui \
+       $(NULL)
 
 -include $(top_srcdir)/git.mk