I agree to the answer of @Charlieface, then if you don't want NULL order_date value in the result you may declare it as IFNULL(order_date, 'any date or value') AS order_date, and for country having NULL values as well IFNULL(country, ''EU' or 'All' or something') AS country.

As a reminder GROUPING SETS intentionally produces NULL values when columns are not included in a particular grouping combination.

Having NULL values is not an error; it's a fundamental part of how GROUPING SETS works.

It is very common to use the COALESCE or IFNULL functions along with GROUPING SETS to convert the null values to another value.