Summary

Mongodb Driver c# 3.x,when aggregate with Builders<BsonDocument>.Projection.Expression, the final pipeline will add $literal operator, which not in 2.28.0.

Please provide the version of the driver. If applicable, please provide the MongoDB server version and topology (standalone, replica set, or sharded cluster).

How to Reproduce

1. Create a Projection
       var projection = Builders<BsonDocument>.Projection.Expression(document => new
           {
               Number = new BsonDocument("$toDouble", new BsonDocument "$substr", new BsonArray {$"${numberFiled}", prefix.Length, -1}),
               Id = document["_id"]
           });
2.  Aggregate with it

dbSet.Aggregate().Project(projection)

Additional Background

Please provide any additional background information that may be helpful in diagnosing the bug.