套接字客户端和服务器java.lang.NumberFormatException：null

Question

例外是在客户端，我试过冲洗但是徒劳无功 这是在客户端

String usn6 = sc.next();
ps.println(usn6);
String po;
try
{
 while(true)
 {
   nf = br.readLine();
   if(Integer.parseInt(nf) == 1)
   {
     System.out.println("FIle not found");
     break;
   }
   else if(Integer.parseInt(nf) == 2)
   {    
       while(true)
       {
            po = br.readLine();
            if(Integer.parseInt(po) == 1)
            {          
              System.out.println(usn6 +" is deleted!");
              break;
            }
            else
            {
              System.out.println("Delete operation is failed.");
              break;

            }
           }
          }
         }

这是服务器端

ps.println("Enter the file name: ");
ps.println("END");
while(true)
{
 filnm = br.readLine();
 System.out.println(filnm);
 File file4 = new File(filnm);
 System.out.println("getting hotter");
 if(!file4.exists())
 {
  System.out.println("getting hotter dude");
  ps.println("1");
  System.out.println("doesnt exist");
  break;
 }
 else
 { 
  ps.print("2");
  ps.flush();
  if(file4.delete())
  {     
   System.out.println("getting hotter daaa");
   ps.println("1");
  }
  else
  {              
   System.out.println("getting crazy daaa");
   ps.println("2");
    }
  }
  break;
 }
}

异常发生在if（Integer.parseInt（nf）== 1）异常为空异常