public function sendEmailReceipt($number, $id = null)
    {
        $this->_requireIdentifier($number, $id);
        return new CheddarGetter_Response(
                                                                                $this->request(
                                                                                    '/invoices/send-email/' . (($id) ? 'id/'.$id : 'number/'.$number),
                                                                                    array(
                                                                                        'bogus' => 'make this a post'
                                                                                    )
                                                                                    )
                                                                                );
    }