code: public String apply(final String word, final String postag) {
      String lemma = null;
      final List<String> keys = this.getDictKeys(word, postag);
      // lookup lemma as value of the map
      final String keyValue = this.dictMap.get(keys);
      if (keyValue != null) {
        lemma = keyValue;
      } else {
        lemma = "O";
      }
      return lemma;
    }
docs: Lookup lemma in a dictionary. Outputs "O" if not found.
  @param word the token
  @param postag the postag
  @return the lemma