var bsonWriter = new BsonBinaryWriter(); bsonWriter.WriteNull();
var bsonDoc = new BsonDocument(); bsonDoc.Add("myField", BsonNull.Value);In this case, the `BsonNull.Value` property is used to represent a null value within a BSON document. In summary, the `MongoDB.Bson.IO` package provides a variety of classes and methods for working with BSON data in C#. In particular, the `BsonWriter` class offers a simple way to write null values to a BSON document, while the `BsonDocument` class provides a more comprehensive interface for working with BSON data as a whole.