Upgrade to Android Oreo and issue with Firebase Cloud Messaging

create a channel id

<string name="default_notification_channel_id" translatable="false">fcm_default_channel</string>

add a meta-data in manifest file

<application>
...
<meta-data        android:name="com.google.firebase.messaging.default_notification_channel_id"
android:value="@string/default_notification_channel_id"/>
</application>

channel assignment

...
// Since android Oreo notification channel is needed.
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.O) {
    String channelId = context.getString(R.string.default_notification_channel_id);
    NotificationChannel channel = new NotificationChannel(channelId,   title, NotificationManager.IMPORTANCE_DEFAULT);
    channel.setDescription(body);
    mNotificationManager.createNotificationChannel(channel);
    builder.setChannelId(channelId);
}
mNotificationManager.notify(1, notification);
...

References
https://medium.com/globallogic-latinoamerica-mobile/firebase-cloud-messaging-warning-updating-to-android-oreo-1343fe894bd5
https://firebase.google.com/docs/cloud-messaging/android/receive