Attempt to invoke virtual method com.google.firebase.iid.FirebaseInstanceId.getInstanceId()' on a null object reference
There was problem in merged manifest, following service was missing from the merged manifest.
Added same to AndroidManifest.xml
it worked like a charm.
<service android:name="com.google.firebase.components.ComponentDiscoveryService" >
<meta-data
android:name="com.google.firebase.components:com.google.firebase.iid.Registrar"
android:value="com.google.firebase.components.ComponentRegistrar" />
</service>
Everything is working fine now.