Caused by: java.lang.NullPointerException: Cannot invoke "dev.instanse.aHub.file.RootFile.getBoolean(String)" because "this.rootdata" is null

Question

This is my code that causes the error:

public void onJoin(PlayerJoinEvent event ){
    Player player = event.getPlayer();

    if (this.rootdata.getBoolean("CustomJoin.custom-message")) {
        final List<String> message = (List<String>)this.langdata.getStringList("CustomJoinMessage.message");
        for (final String send : message) {
            MsgUtil.sendMessage(player, send);
        }
    }
}