如何在C＃中修复NullReferenceException？

Question

我在制作一个简单的程序时非常擅长编码并陷入困境。我想要做的是从.txt文件中读取数据并将其添加到类数组中，所以当我输出studClasses [0] .Days [0] .Lesson [1]时，它会显示＆＃34;数学＆＃ 34;等等。 问题是，我不知道如何解决问题，排在第一位[a] .Days [i] .AddLesson（line）;＆＃34;

static void Main(string[] args)
{
    int CMax = 50;
    StudentClass[] studClasses = new StudentClass[CMax];
    ReadData(file, studClasses);
}
public class StudentClass
{
    public const int CMax = 50;
    public Day[] Days { get; set; }
    public string ClassName { get; set; }

    public StudentClass()
    {
        ClassName = "";
        Day[] Days = new Day[CMax];
    }
    public void AddClass(string cls)
    {
        ClassName = cls;
    }
}

public class Day
{
    public const int CMax = 100;
    public string[] Lessons { get; set; }
    public int lessonNumber { get; set; }

    public Day(string[] less)
    {
        Lessons = less;
    }
    public void AddLesson(string lesson)
    {
        Lessons[lessonNumber] = lesson;
        lessonNumber++;
    }
}
private static void ReadData(string file, StudentClass[] studClasses)
{       
    using (StreamReader reader = new StreamReader(@file))
    {
        int a = 0;
        string line = null;
        while (null != (line = reader.ReadLine()))
        {
            for (int i = 0; i < 5; i++) // 5 days Monday-Friday
            {
                for (int j = 0; j < 7; j++) // 7 lessons each day
                {
                    line = reader.ReadLine();
                    studClasses[a].Days[i].AddLesson(line);
                }
            }
            a++;
        }
    }       
}

提前感谢您的帮助！ 编辑：错误代码：未处理的类型＆＃39; System.NullReferenceException＆＃39;发生在ConsoleApplication1.exe中 附加信息：未将对象引用设置为对象的实例 EDIT2：添加了对ReadData的调用。