inapp purchase verifyreceipt status = 21002

1. i was developing in app purchase app.i was created test account in my apple id.
   


2. inapp purchase app is tested in device
   


3. i was entered test account details in inapp purchase application.transactions are completed
   


4. if i verify receipt in sandboxurl:https://sandbox.itunes.apple.com/verifyReceipt
   

1. 
   

   
   i got a error receipt like this format
   

   
   

   
   
   
   exception = "java.lang.NullPointerException";
   
   status = 21002;
   
   
   
   

   
   

   
   please help me.