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