String result = popularWordHelper.getCacheKey(seed, tags, roles, fields, excludes);

        assertNotNull(result);
        assertTrue(result.startsWith("null"));
    }

    public void test_getCacheKey_specialCharacters() {
        String seed = "test@seed#with$special%chars";
        String[] tags = { "tag@1", "tag#2" };
        String[] roles = { "role$1", "role%2" };
        String[] fields = { "field&1", "field*2" };