code: private void clearDeck(CdjStatus update) {
          if (hotCache.remove(DeckReference.getDeckReference(update.getDeviceNumber(), 0)) != null) {
              deliverTrackMetadataUpdate(update.getDeviceNumber(), null);
          }
      }
docs: We have received an update that invalidates any previous metadata for that player, so clear it out, and alert
  any listeners if this represents a change. This does not affect the hot cues; they will stick around until the
  player loads a new track that overwrites one or more of them.
  
  @param update the update which means we can have no metadata for the associated player