Why i am getting a Number FormatException?

I made a program on the code chef.I am getting a correct output on my eclipse ide and when i submitted it the output shown on CodeChef ide is :

Exception in thread "main" java.lang.NumberFormatException: null
at java.lang.Integer.parseInt(Integer.java:542)
at java.lang.Integer.parseInt(Integer.java:615)
at Prog1.stop(Main.java:16)
at Prog1.main(Main.java:50)

Here is the question Link:https://www.codechef.com/problems/TEST

Here is my solution to the problem: //life universe and EveryThing

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

class Prog1 
{
 public static void stop() throws IOException
 {

   BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
   String s1=br.readLine();
   int x=Integer.parseInt(s1);
   int ar[]=new int[x];
   int k=0;
    for(int i=0;i<x;i++)
     {
       BufferedReader br1=new BufferedReader(new InputStreamReader(System.in));
       String s2=br1.readLine();
       int p=Integer.parseInt(s2);
       ar[k++]=p;
     }
   for(int m=0;m<x;m++)
    {
       System.out.println(ar[m]);
    }
   for(int y=0;y<x;)
    {
        if(ar[y]!=42)
        {
          System.out.println(ar[y]);
          y++;
        }
        else
        {
          break;
        }

    }

}
 public static void main(String s[]) throws IOException
 {
 stop();
 }
}