How to enable Firebase Crash Reporting - Android

I followed all the steps on the docs to use Firebase Crash Reporting in my Android app (I use Android Studio and everything is up-to-date).

I used their own code to throw an exception to see if it works:

try {
    throw new NullPointerException();
} catch (NullPointerException ex) {
    FirebaseCrash.logcat(Log.ERROR, TAG, "NPE caught");
    FirebaseCrash.report(ex);
}

And the console gives me this log:

E/MainActivity: NPE caught

V/FirebaseCrash: Firebase Crash Reporting is disabled.

So, the thing is how can I enable it?

NOTE: I have all of the dependencies added including the crash and core ones, also the plugin and the classpath

Thank you in advanced.