.net反射问题

如题 求教————————
请测试以下代码 
using System;
using System.Collections.Generic;
using System.Text;using System.Reflection;
namespace BubbleSort.io
{
    public class ReflectionHelper
    {
        private Data data = new Data();
        public void ListMember()
        {
            Console.WriteLine("-----遍历反射对象-----");
            Console.WriteLine("成员名\t\t成员类型\t\t声明成员类");
            MemberInfo[] arr = data.GetType().GetMembers();
            foreach (MemberInfo var in arr)
            {
                Console.WriteLine(string.Format("{0}\t{1}\t{2}", var.Name.PadRight(10, ' '), var.MemberType.ToString().PadLeft(10, ' '), var.DeclaringType.ToString().PadLeft(10, ' ')));            }        }
        public void ListScore()
        {
            Console.WriteLine("------成绩数据------");
            Console.WriteLine("姓名\t\t性别\t\t课程名\t\t教授\t\t成绩");
            FieldInfo[] arr = data.GetType().GetFields();
            foreach (FieldInfo var in arr)
            {
                Score score = (Score)var.GetValue(data);
                Console.WriteLine(string.Format("{0},{1},{2},{3},{4}",score.student.studentName,score.student.studentGender,score.course.courseName,score.course.courseTeacherName,score.));            }
        }
    
        
        
        }
    }
    public class Data
    {
        public Score score1;
        public Score score2;
        public Score score3;
        public Score score4;
        private Student stu1;
        private Student stu2;
        private Course cou1;
        private Course cou2;
        public Student Stu1 
        
        {
            get { return stu1; }
            set { value = stu1; }
        
        
        }
        public Student Stu2 
        {
            get { return stu2; }
            set { value = stu2; }
        
        }
        public Data()
        {            stu1 = new Student("小李",Gender.男);
            stu2 = new Student("小明",Gender.女);
            cou1 = new Course("课程A","Jession");
            cou2 = new Course("课程B","LG");
            score1 = new Score(stu1,cou1,90);
            score2 = new Score(stu1,cou2,80);
            score3 = new Score(stu2, cou1, 100);
            score4 = new Score(stu2,cou2,100);        
          
        
        }
          
        public Course GetCourse1()
        {
            return cou1;
        
        
        
        
        }
        public Course GetCourse2() 
        {
            return cou2;
        }
    
    
    
    }
    public enum Gender{男,女}
    public class Student
    {        public string studentName;
        public Gender studentGender;        public Student(string nStudentName,Gender nStudentGender)
        {
            studentName = nStudentName;
            studentGender = nStudentGender;        
        
        
        }
    
    
    
    }
    public class Course 
    {
        public string courseName;
        public string courseTeacherName;
        public Course(string sCourseName,string sCourseTeacherName)
        {
            courseName = sCourseName;
            courseTeacherName = sCourseTeacherName;
        
        
        
        }    
    
    }
    public class Score
    {
        public Student student;
        public Course course;
        public int ;
        public Score(Student nStudent,Course nCourse,int nMark)
        {
            nStudent = student;
            nCourse = course;
             = nMark;
        
        
        }    
    
    
    }为什么报出nullflectionExptions的错误来 请大虾详细解释下