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);

    var cluster = client.Cluster;
    using(var session = cluster.StartSession())
    using (var writeBinding = new WritableServerBinding(cluster, session))
    {
        return await op.ExecuteAsync(writeBinding, CancellationToken.None);
    }
  }
}