code: @Nullable
      public String get(int n) {
          if (capitalword_) return null;
          int len = grams_.length(); 
          if (n < 1 || n > N_GRAM || len < n) return null;
          if (n == 1) {
              char ch = grams_.charAt(len - 1);
              if (ch == ' ') return null;
              return Character.toString(ch);
          } else {
              return grams_.substring(len - n, len);
          }
      }
docs: TODO this method has some weird, undocumented behavior to ignore ngrams with upper case.
  
  Get n-Gram
  @param n length of n-gram
  @return n-Gram String (null if it is invalid)