src/main/java/com/github/phantomthief/util/MoreCollectors.java
@Deprecated
    public static <T, K, U, M extends Multimap<K, U>> Collector<T, ?, M> toMultimap(
            Function<? super T, ? extends K> keyMapper,
            Function<? super T, ? extends U> valueMapper, Supplier<M> supplier) {
        BiConsumer<M, T> accumulator = (multimap, element) -> multimap.put(keyMapper.apply(element),
                valueMapper.apply(element));
        BinaryOperator<M> finisher = (m1, m2) -> {
            m1.putAll(m2);
            return m1;
        };
        return new CollectorImpl<>(supplier, accumulator, finisher, CH_ID);
    }
@Deprecated
    public static <T, K, U, M extends Multimap<K, U>> Collector<T, ?, M> toMultimap(
            Function<? super T, ? extends K> keyMapper,
            Function<? super T, ? extends U> valueMapper, Supplier<M> supplier) {
        BiConsumer<M, T> accumulator = (multimap, element) -> multimap.put(keyMapper.apply(element),
                valueMapper.apply(element));
        BinaryOperator<M> finisher = (m1, m2) -> {
            m1.putAll(m2);
            return m1;
        };
        return new CollectorImpl<>(supplier, accumulator, finisher, CH_ID);
    }
use {@link com.google.common.collect.Multimaps#toMultimap(Function, Function, Supplier)} if using guava 21.0+