public function __isset( $key ) {
		$legacy_keys = array(
			'id',
			'country',
			'state',
			'postcode',
			'city',
			'address_1',
			'address',
			'address_2',
			'shipping_country',
			'shipping_state',
			'shipping_postcode',
			'shipping_city',
			'shipping_address_1',
			'shipping_address',
			'shipping_address_2',
			'is_vat_exempt',
			'calculated_shipping',
		);
		$key = $this->filter_legacy_key( $key );
		return in_array( $key, $legacy_keys );
	}