Weaviate GraphQL - How to Group by Multiple Properties

Question

I have an object News in Weaviate with a year, a month, a day and some other data columns. I want to count the rows per year and month. In SQL this would look like this:

SELECT year, month, count(*) FROM news group by year, month;

In Weaviate GraphQL I only managed to group by one column.

{
  Aggregate {
    News (groupBy:["month"]) {
        groupedBy {
              path
            value
        }
        meta {
            count
        }
    }
  }
}

Unfortunately the Weaviate documentation misses out this issue.

What is the correct way to group by multiple fields in Weaviate GraphQL? (PS: in fact I need to implement this in Python using the weaviate-client-api)