Multiverse Core not found

private void loadMultiverseCore() {
    Plugin multiversePlugin = getServer().getPluginManager().getPlugin("Multiverse-Core");
    if (multiversePlugin instanceof MultiverseCore) {
        MVWorldManager = ((MultiverseCore) multiversePlugin).getMVWorldManager();
    } else {
        throw new RuntimeException("Multiverse-Core not found!");
    }
}