[vala] codegen: Guard target_value to be non-null in visit_expression

[Luca Bruno <lucabru src gnome org>]

commit e76634f952e7d622b71e2001249e9ddc37003fe8
Author: Luca Bruno <lucabru src gnome org>
Date:   Sat Aug 27 16:30:45 2011 +0200

    codegen: Guard target_value to be non-null in visit_expression
    
    Fixes bug 657499.

 codegen/valaccodebasemodule.vala |    4 ++++
 1 files changed, 4 insertions(+), 0 deletions(-)
---
diff --git a/codegen/valaccodebasemodule.vala b/codegen/valaccodebasemodule.vala
index a62c6ea..e9c9a7a 100644
--- a/codegen/valaccodebasemodule.vala
+++ b/codegen/valaccodebasemodule.vala
@@ -3476,6 +3476,10 @@ public abstract class Vala.CCodeBaseModule : CodeGenerator {
 				expr.target_value = transform_value (expr.target_value, expr.target_type, expr);
 			}
 
+			if (expr.target_value == null) {
+				return;
+			}
+
 			if (expr.formal_target_type is GenericType && !(expr.target_type is GenericType)) {
 				if (expr.formal_target_type.type_parameter.parent_symbol != garray_type) {
 					// GArray doesn't use pointer-based generics