The attached Program.cs fails with the message:

Message=Command 'mapreduce' failed: db assertion failure (response: { "assertion" : "could not create cursor over test.test for query : { B:

} sort :

", "assertionCode" : 15876, "errmsg" : "db assertion failure", "ok" : 0.0 })

The code is based on the official test TestMapReduceInlineWithQuery. Perhaps
the problem can be seen just there if the line

var result = _collection.MapReduce(query, map, reduce);

is replaced with

var options = new MapReduceOptionsBuilder();
options.SetQuery(query);
options.SetOutput(MapReduceOutput.Inline);
options.SetSortOrder((new SortByBuilder()).Ascending("B"));
var result = _collection.MapReduce(map, reduce, options);

If I remove the line with SetSortOrder then the code works fine.

Sorry if I just do something wrong and this is a false alarm. I asked the
question at the forum but did not get the answer.