public static <T, U> BiFunction<T, U, Void> voidFunction(BiConsumer<T, U> consumer) {
        requireNonNull(consumer, "consumer");
        return (a, b) -> {
            consumer.accept(a, b);
            return null;
        };
    }
Converts the specified {@link BiConsumer} into a {@link BiFunction} that returns {@code null}.
core/src/main/java/com/linecorp/armeria/common/util/Functions.java