Am trying out the recently released feature that allows uploading of ProGuard mapping file to Firebase (https://firebase.google.com/docs/crash/android) using gradle task. T
The error message is misleading. You will see that if the file path that you give for the service account wasn't found. Try passing the full, unambiguous path of the service account file (try not to depend on relative paths).
I'll make sure that the next version of the plugin has a more meaningful error message for the case where the file isn't found. Sorry about the trouble.