Serializable extra is lost on Android 7.1 PendingIntent

Question

I have written code which shows a notification when an SMS has been sent.

For some reason the code does not work on Android 7 like on all lower API levels.

The second parameter (contact) is lost and retrieved as null in the CompletedReceiver class.

Here is my code:

SendMessage method

    private static void sendMessage(Context context, Message message, SystemContact contact) {
        SmsManager smsManager = SmsManager.getDefault();

// Create sent intent.
Intent sentIntent = new Intent(context, SmsController.SendResultReceiver.class);
        sentIntent.putExtra(context.getString(R.string.key_message_id), message.getId());
    sentIntent.putExtra(context.getString(R.string.key_contact), contact);

    PendingIntent pendingIntent = PendingIntent.getBroadcast(context, RequestCodes.SENT_SMS, sentIntent, PendingIntent.FLAG_UPDATE_CURRENT);
    smsManager.sendTextMessage(contact.getPhoneNr(), null, message.getMsg(), pendingIntent, null);
}

CompletedReceiver

private void initPassedData(Context context, Intent intent) {
        this.message = IntentHelper.getMessageById(context, intent);
        this.contact = (SystemContact) intent.getSerializableExtra(context.getString(R.string.key_contact));
    }

Also what does the PendingIntent.FLAG_UPDATE_CURRENT mean?