code: @Override
      public SubscriberState getState(int id) {
          if (!statusStorageMap.containsKey(id))
              return SubscriberState.empty();
          return statusStorageMap.get(id);
      }
docs: Get the state given an id.
  The integer represents a stream id
  for a given {@link ParameterServerSubscriber}.
  <p>
  A {@link SubscriberState} is supposed to be 1 to 1 mapping
  for a stream and a {@link MediaDriver}.
  
  @param id the id of the state to get
  @return the subscriber state for the given id or none
  if it doesn't exist