Make sure to call FirebaseApp.initializeApp(Context) first. Default FirebaseApp is not initialized in this process com.example.login

I had something similar because I forgot about adding

apply plugin: 'com.google.gms.google-services'

on bottom of build.gradle

Thanks everyone but I solved it myself. All I did is

classpath 'com.google.gms:google-services:4.1.0'

to

classpath 'com.google.gms:google-services:4.2.0'

That worked for me!