Publishing ODK Collect on Playstore

I've cloned the ODK collect and have made some of custom changes required for my project. But changing package name urges me to change in google-service.json file too. And when I try to get the form from the app, it throws me an exception with a message

Attempt to invoke interface method 'int android.database.Cursor.getCount()' on a null object reference

A help would be appreciated for a better approach to change the package name and use the functionalities of ODK Collect