public static <K, V> Collector<Map.Entry<? extends K, ? extends V>, ImmutableMap.Builder<K, V>, ImmutableMap<K, V>> toMap() {
        //noinspection unchecked
        return (Collector) MAP;
    }
Immutable implementations of {@link Collector} using Guava's immutable collections.
helper/src/main/java/me/lucko/helper/utils/ImmutableCollectors.java