code: private final void checkTopicNotNull(String topic) 
      throws InvalidTopicSyntaxException
    {
      if (topic == null)
        throw new InvalidTopicSyntaxException(
          NLS.format(
            "INVALID_TOPIC_ERROR_CWSIH0005",
            new Object[] { topic }));
    }
docs: null topic check
  
  @param topic  The topic to be checked.
  
  @throws InvalidTopicSyntaxException if the topic is null