protected function get_address_prop( $prop, $address = 'billing', $context = 'view' ) {
        $value = null;

        if ( array_key_exists( $prop, $this->data[ $address ] ) ) {
            $value = isset( $this->changes[ $address ][ $prop ] ) ? $this->changes[ $address ][ $prop ] : $this->data[ $address ][ $prop ];