code: public boolean isNewSession() {
          Session session = handlerInput.getRequestEnvelope().getSession();
          if (session == null) {
              throw new IllegalArgumentException("The provided request doesn't contain a session");
          }
          return session.getNew();
      }
docs: Returns whether the request is a new session.
  
  The method retrieves the new value from the input request's session, which indicates if it's a new session or
  not. More information can be found here :
  https://developer.amazon.com/docs/custom-skills/request-and-response-json-reference.html#session-object
  
  This method returns an {@link IllegalArgumentException} if the request is not an in-session request.
  
  @return true if the request is a new session