@Test
public void dictsToTrie_empty_dicts_should_return_null() throws Exception {

    List<PinyinDict> dicts = new ArrayList<PinyinDict>();
    dicts.add(new PinyinMapDict() {
        @Override
        public Map<String, String[]> mapping() {
            return null;
        }
    });
    assertThat(Utils.dictsToTrie(dicts), nullValue());
}