The `account_tax_rule_country` module extends different document to extend pattern values for countries (like sale and purchase) and set the value as `None` if it can not be determined. But there are cases like in `WebShop.get_products()` where any country can be guessed. So the result is that the first matching rule with or without a country is used. This may be wrong as usually users rely on no rule to be applied by default. So I think we should always add by default `None` to the countries pattern and not rely on the module extending all the call to `TaxRule.apply()`.