谁能帮忙解决这个问题 空指针异常

package com.XuanKe;

import java.util.Arrays;
import java.util.Iterator;
import java.util.List;
import java.util.ArrayList;

/**
 * 备选课
 * @author Administrator
 *
 */
public class BeiXUanKeTest {
 private List CourseToSelect;

 public List getCourseToSelect() {
  return CourseToSelect;
 }
 public void setCourseToSelect(List courseToSelect) {
  this.CourseToSelect = new ArrayList();
 }
 @SuppressWarnings("unchecked")
 public void CourseAdd(){//添加备选课程
  Course cr1=new Course();
  cr1.setId("1");
  cr1.setName("数据结构");
  CourseToSelect.add(cr1);
  Course temp =(Course) CourseToSelect.get(0);
  System.out.println("添加课程为："+temp.getId()+" :"+temp.getName());
  
  
  Course cr2=new Course();
  cr2.setId("2");
  cr2.setName("C语言");
  CourseToSelect.add(0, cr2);
  Course temp2=(Course) CourseToSelect.get(1);
  System.out.println("添加课程为："+temp2.getId()+"　："+temp2.getName());
  
  //数组添加课程
  Course cr3=new Course();
  cr3.setId("3");
  cr3.setName("离散数学");
  Course cr4=new Course();
  cr4.setId("4");
  cr4.setName("汇编语言");
  Course[] course={cr3,cr4};
  CourseToSelect.addAll(Arrays.asList(course));
  Course temp3 =(Course) CourseToSelect.get(2);
  Course temp4 =(Course) CourseToSelect.get(3);
  System.out.println("添加课程为："+temp3.getId()+" "+temp3.getName()+" "+temp4.getId()+" "+temp4.getName());
  
  
  Course cr5=new Course();
  cr5.setId("5");
  cr5.setName("高等数学");
  Course cr6=new Course();
  cr6.setId("6");
  cr6.setName("大学英语");
  Course[] course1={cr5,cr6};
  CourseToSelect.addAll(2,Arrays.asList(course1));
  Course temp5 =(Course) CourseToSelect.get(2);
  Course temp6 =(Course) CourseToSelect.get(3);
  System.out.println("添加课程为："+temp5.getId()+" "+temp5.getName()+" "+temp6.getId()+" "+temp6.getName());
  
 }
 //输出备选课程
 public void getBeiXuan(){
  //用数组
  System.out.println("有如下备选课：");
  for(int i=0;i<CourseToSelect.size();i++){
   CourseToSelect.get(i);
   Course cr=(Course) CourseToSelect.get(i);
   System.out.println("课程："+cr.getId()+":"+cr.getName());
  }
  //用迭代器
  System.out.println("有如下备选课（迭代器）：");
  Iterator it=CourseToSelect.iterator();
  while(it.hasNext()){
   Course cr=(Course) it.next();
   System.out.println("课程："+cr.getId()+":"+cr.getName());
  }
  //foreaach
  System.out.println("有如下备选课（foreach）：");
  for(Object obj:CourseToSelect){
   Course cr=(Course) obj;
   System.out.println("课程"+cr.getId()+" :"+cr.getName());
  }
 }
 public static void main(String[] args) {
  BeiXUanKeTest bx=new BeiXUanKeTest();
  bx.CourseAdd();
  bx.getBeiXuan();
 }
 
}

package com.XuanKe;

import java.util.HashSet;
import java.util.Set;
/**
 * 学生类
 * @author Administrator
 *
 */
public class Student {
 private String id;
 private String name;
 private Set course;
 public String getId() {
  return id;
 }
 public void setId(String id) {
  this.id = id;
 }
 public String getName() {
  return name;
 }
 public void setName(String name) {
  this.name = name;
 }
 public Set getCourse() {
  return course;
 }
 public void setCourse(Set course) {
  this.course = new HashSet();
 }
 
}

package com.XuanKe;
/**
 * 课程类
 * @author Administrator
 *
 */
public class Course {
 private String id;
 private String name;
 public String getId() {
  return id;
 }
 public void setId(String id) {
  this.id = id;
 }
 public String getName() {
  return name;
 }
 public void setName(String name) {
  this.name = name;
 }
}