无法在c#中获取mongodb聚合查询结果

using MongoDB.Bson;
using MongoDB.Driver;

var connectionString = "mongodb://localhost:27017";
var client = new MongoClient(connectionString);
var database = client.GetDatabase("your-database-name");

var collection = database.GetCollection<BsonDocument>("your-collection-name");

var pipeline = new BsonDocument[]
{
    new BsonDocument("$match", new BsonDocument("field", "value")),
    new BsonDocument("$group", new BsonDocument("_id", "$field")),
    new BsonDocument("$project", new BsonDocument("field1", 1))
};

var result = collection.Aggregate(pipeline).ToList();