[vala] Fix assigning null to GVariant variable

[Jürg Billeter <juergbi src gnome org>]

commit a7767b292bdb27be8e830060b25b0ecb211c9c49
Author: Jürg Billeter <j bitron ch>
Date:   Mon Jun 28 23:38:30 2010 +0200

    Fix assigning null to GVariant variable

 codegen/valaccodebasemodule.vala |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)
---
diff --git a/codegen/valaccodebasemodule.vala b/codegen/valaccodebasemodule.vala
index 031c5d2..cdb90c6 100644
--- a/codegen/valaccodebasemodule.vala
+++ b/codegen/valaccodebasemodule.vala
@@ -4991,6 +4991,7 @@ public class Vala.CCodeBaseModule : CCodeModule {
 		bool gvariant_boxing = (context.profile == Profile.GOBJECT
 		                        && target_type != null
 		                        && target_type.data_type == gvariant_type
+		                        && !(expression_type is NullType)
 		                        && expression_type.data_type != gvariant_type);
 
 		if (expression_type.value_owned