code: public CharSequence buildCharSequence(StringTrieBuilder.Option buildOption) {
          buildChars(buildOption);
          return CharBuffer.wrap(chars, chars.length-charsLength, charsLength);
      }
docs: Builds a CharsTrie for the add()ed data and char-serializes it.
  Once built, no further data can be add()ed until clear() is called.
  
  <p>A CharsTrie cannot be empty. At least one (string, value) pair
  must have been add()ed.
  
  <p>Multiple calls to build() or buildCharSequence() return tries or sequences
  which share the builder's char array, without rebuilding.
  After clear() has been called, a new array will be used.
  @param buildOption Build option, see StringTrieBuilder.Option.
  @return A CharSequence with the char-serialized CharsTrie for the add()ed data.