public List <string> GetSentenceLemmas(string sentence, char separator = ' ')
        {
            try {
                LoadIfNeed();

                var    result = new HashSet <string>();
                var    buffer = new StringBuilder();
                IntPtr hList  = LemmatizatorEngine.sol_LemmatizePhraseW(_hEngine, sentence, LemmatizatorEngine.LEME_DEFAULT, separator);
                return(AddLemmasToResult(hList, buffer, result));
            } catch (Exception e) {
                return(null);
            }
        }