Fill in missing dates in google sheet query

I have a google sheet query like this:

=QUERY(A2:I;"select I, sum(C) * -1, count(C) group by I order by I ASC"; 1)

And it yield a result like this:

In the source data not all months are occur. But in the aggregation I want to see all the months. How can I manipulate the results or the query, so I have all the monhts. See example output:

BTW: If you are asking why 2020-11 is showing up. This is due to the fact that in this month there was exacly the same ammount of negative and positive, resulting in 0