code: private List<String> getDictKeys(final String word, final String postag) {
      final List<String> keys = new ArrayList<String>();
      keys.addAll(Arrays.asList(word.toLowerCase(), postag));
      return keys;
    }
docs: Generate the dictionary keys (word, postag).
  
  @param word
  the surface form
  @param postag
  the assigned postag
  @return a list of keys consisting of the word and its postag