I have a problem with aggregation pipeline using C# drivers.
I am trying to build Project() stage and use $reduce inside (trying to rewrite example from Question no. 3 from Final Exam in Aggregation Framework).
The problem is when I am trying to use $$value inside BsonArray.
Such an error appeared:
Besides this little part of aggregation pipeline other steps of the pipeline works well in insolation.
Did anyone encounter such problem before ? Am I doing something wrong?