function testToXmlWithNull()
    {
        $data = null;
        $t = new TransactionTypes();
        $parent = XmlSerializer::createDocument('transaction_types');
        $t->toXml($data, $parent);
        $this->assertEqual($parent->ownerDocument->saveXml(), '<?xml version="1.0" encoding="UTF-8"?>
<transaction_types/>
');
    }