missed null check in refactoring

src/lib/objects/o_closure.c

@@ -72,7 +72,7 @@ static Object *select_(Object *self, Object *key,
 	if(err->occurred)
 		return NULL;
 
-	if (selected == NULL)
+	if (selected == NULL && closure->prev != NULL)
 		selected = Object_Select(closure->prev, key, heap, err);
 
 	return selected;
@@ -82,6 +82,6 @@ static void walk(Object *self, void (*callback)(Object **referer, void *userp),
 {
 	ClosureObject *closure = (ClosureObject*) self;
 
-	callback((Object**) &closure->prev, userp);
+	callback(&closure->prev, userp);
 	callback(&closure->vars, userp);
 }