[rules-users] Null Pointer Exception

Hi, I am using eclipse IDE for Drools. I am new to Drools so just trying adding to numbers if they are other then zero, but I am getting Null Pointer Exception . rule add salience 10 when a1 : AddNumber ( op1 != 0 ) a2: AddNumber ( op2 != 0 ) then a1.setResult( a1.getOp1() + a2.getOp2() ); System.out.println( "Result is "+a1.getResult()); End Regards Shilpa The information contained in this electronic message and any attachments to this message are intended for the exclusive use of the addressee(s) and may contain proprietary, confidential or privileged information. If you are not the intended recipient, you should not disseminate, distribute or copy this e-mail. Please notify the sender immediately and destroy all copies of this message and any attachments. WARNING: Computer viruses can be transmitted via email. The recipient should check this email and any attachments for the presence of viruses. The company accepts no liability for any damage caused by any virus transmitted by this email. www.wipro.com