nodejs pm2 --merge-logs with -l option

I am using pm2 to deploy nodejs application. Here is my syntax

NODE_ENV=production pm2 start server.js --name "demoapp" --merge-logs -l "/var/log/demoapp/demo-application.log"

But it is not able to start the application. If I remove the --merge-logs option application starts and logs are generated with suffix(PID).

I want logs to be generated without suffix.

via dkakoti