AWS Lambda giving Error: Invalid 'keyPath' option

I want to publish messages from AWS Lambda(Nodejs ) to mqtt topic and is using “aws-iot-device-sdk” .
I am deploying code as zip folder in lambda function and is getting “Error: Invalid ‘keyPath’ option supplied” while i have pem.key (Keys , certificates ,root ca for accessing IOT) file present it in same folder.The code is working fine when trying in sublime text