MythicMobSpawnEvent Bug (Version 5..0.0 free)

    @EventHandler
    public void onSpawn(MythicMobSpawnEvent event){
    getLogger().log(Level.INFO,event.isFromMythicSpawner().toString());
}

I'm trying to detect whether the mob comes out from a MythicMobSpawner. but it doesn't seem to work the outcome of event.getMythicSpawner is always null , whether the mob is spawned from a spawner.