将对象添加到构造函数中的arraylist

Question

我正在尝试编译并运行此代码，我已经在非常类似的线程中尝试了一个解决方案，但我仍然得到错误。在另一个帖子中发布的解决方案是使用“.add（this）”。

import java.util.ArrayList;
import java.util.Arrays;
public class Chore implements Priority{

    private String description;
    private int priority;
    private boolean completed;
    private static ArrayList<Chore> chores;
    public Chore(){

        String choreArr[] = {"Mow the lawn", "Fold the laundry", "Make dinner", "Vacuum the house"};
        int randChore = (int)(Math.random()*4);
        int randPri = (int)(Math.random()*10)-1;
        description = choreArr[randChore];
        priority = randPri;
        chores.add(this);
    }
    public Chore(int i, String s){
        priority = i;
        description = s;
        chores.add(this);
        }

    public void setComplete(){
        completed = true;
    }
    public void setPriority(int p){
        priority = p;
    }
    public int getPriority(){
        return priority;
    }
    public String toString(){
        return description + ": " + completed;
    }
    public int compare(Chore cC){
        return priority - cC.priority;
    }

    public static String doFirst(){
        Chore[] copy = new Chore[chores.size()];
        chores.toArray(copy);
        Arrays.sort(copy);
        return copy[copy.length -1].description;
     }
   }

当我尝试创建Chore对象时，我收到以下错误 Exception in thread "main" java.lang.NullPointerException at Chore.<init>(Chore.java:16)