using System;

using System.Collections.Generic;

using System.Linq;

using YamlDotNet.Core;

using YamlDotNet.Core.Events;

using YamlDotNet.Serialization;

using YamlDotNet.Serialization.EventEmitters;

​

public class Program

{

    public static void Main(string[] args)

    {

        var serializer = new SerializerBuilder()

            .WithEventEmitter(nextEmitter => new NullStringsAsEmptyEventEmitter(nextEmitter))

            .Build();

        var yaml = serializer.Serialize(new[] { "one", null, "three" });

        Console.WriteLine(yaml);

    }

}

​

public class NullStringsAsEmptyEventEmitter : ChainedEventEmitter

{

    public NullStringsAsEmptyEventEmitter(IEventEmitter nextEmitter)

        : base(nextEmitter)

    {

    }

​

    public override void Emit(ScalarEventInfo eventInfo, IEmitter emitter)

    {

        if (eventInfo.Source.Type == typeof(string) && eventInfo.Source.Value == null)

        {

            emitter.Emit(new Scalar(string.Empty));

        }

        else

        {

            base.Emit(eventInfo, emitter);

        }

    }

}