code: public char getStopKey() {
          String value = Optional.fromNullable(getParameter(SignalParameters.STOP_KEY.symbol())).or("");
          return value.isEmpty() ? ' ' : value.charAt(0);
      }
docs: Defines a key with the following action. Terminate playback of the announcement.
  <p>
  <b>No default.</b>
  </p>
  
  @return