public static <K, V> String toMap(final Supplier<MultiValueMap<K, V>> supplier) {
        return GsonUtils.getInstance().toJson(supplier.get().toSingleValueMap());
    }
@Test
    public void testToMap() {
        final MultiValueMap<String, String> args = new LinkedMultiValueMap<>();
        args.add("a", "1");
        args.add("a", "2");
        args.add("b", "3");
        String actual = HttpParamConverter.toMap(() -> args);
        assertEquals("{\"a\":\"1\",\"b\":\"3\"}", actual);
    }