序列化 XML 时出现 System.NullReferenceException [duplicate]

问：

我想像下面一样序列化简单的类并写入XML文件。

示例类文件：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace SampleXMLSerializeDeserialize
{
    public class SampleXML
    {
        public SampleXML()
        {

        }
        public List<IndividualInfo> IndividualInfo { get; set; }
        public List<CommunicationInfo> Communication { get; set; }
    }

    public class IndividualInfo
    {
        public String Name { get; set; }
        public String Age { get; set; }
    }

    public class CommunicationInfo
    {
        public String presentAdd { get; set; }
        public String permanentAdd { get; set; }
    }
}

序列化方法：

namespace SampleXMLSerializeDeserialize
{
    class Program
    {
        static void Main(string[] args)
        {
            SampleXML s = new SampleXML();
            s.IndividualInfo[0].Name="Jyoti";
            s.IndividualInfo[0].Age = "25";

            s.Communication[0].permanentAdd = "Dhaka";
            s.Communication[0].presentAdd = "Dhaka";
            XmlSerializer serializer = new XmlSerializer(typeof(SampleXML));
            StreamWriter str = new StreamWriter(Environment.GetFolderPath(System.Environment.SpecialFolder.MyDocuments) + @"\SAM.XML");
            serializer.Serialize(str, s);
        }
    }
}

我在以下行获得System.NullReferenceExeption：s.IndividualInfo[0]。名称=“Jyoti”;

你能帮帮忙吗，我错过了什么