MongoClient C# Eval Implementation

MongoEvalExtensions.cs

public static class MongoClientExtensions
{
  /// <summary>
  /// Evaluates the specified javascript within a MongoDb database
  /// </summary>
  /// <param name="database">MongoDb Database to execute the javascript</param>
  /// <param name="javascript">Javascript to execute</param>
  /// <returns>A BsonValue result</returns>
  public static async Task<BsonValue> EvalAsync(this IMongoDatabase database, string javascript)
  {
    var client = database.Client as MongoClient;

    if (client == null)
        throw new ArgumentException("Client is not a MongoClient");

    var function = new BsonJavaScript(javascript);
    var op = new EvalOperation(database.DatabaseNamespace, function, null);

    using (var writeBinding = new WritableServerBinding(client.Cluster, new CoreSessionHandle(NoCoreSession.Instance)))
    {
        return await op.ExecuteAsync(writeBinding, CancellationToken.None);
    }
  }
}

This piece of code doesn't work anymore with MongoDB 4.0.0+, $eval was dropped.
See https://www.mongodb.com/blog/post/going-in-mongodb-42#:~:text=Eval%20has%20left%20the%20building&text=What's%20changed%20in%20MongoDB%204.2,all%20operations%20on%20the%20database..

Thanks, @TomyCesaille. It was good while it lasted.

Are you aware of a possible alternative to this ?
Would like to run a command like so:

db.loadServerScripts();
addFunction(1,2); // -> 3

where addFunction is defined like so:

// to add a function
db.system.js.insertOne(
   {
     _id : "addFunction" ,
     value : function (x, y){ return x + y; }
   }
);

Does the c# driver support multi line statements ?