code: @Override
  	public String parse(JsonPullParser parser, OnJsonObjectAddListener listener)
  			throws IOException, JsonFormatException {
  		if (parser == null) {
  			throw new IllegalArgumentException();
  		}
  
  		State state = parser.getEventType();
  
  		switch (state) {
  			case VALUE_NULL:
  				return null;
  			case VALUE_STRING:
  				return parser.getValueString();
  			default:
  				throw new IllegalStateException();
  		}
  	}
docs: {@inheritDoc}