public String appendTo(String url) {
        Preconditions.checkNotNull(url, "Cannot append to null URL");
        final String queryString = asFormUrlEncodedString();
        if (queryString.equals(EMPTY_STRING)) {
            return url;
        } else {
            return url
                    + (url.indexOf(QUERY_STRING_SEPARATOR) == -1 ? QUERY_STRING_SEPARATOR : PARAM_SEPARATOR)
                    + queryString;
        }
    }
@Test
    public void shouldAppendNothingToQuerystringIfGivenEmptyMap() {
        final String url = "http://www.example.com";
        Assert.assertEquals(url, params.appendTo(url));
    }