code: private void clearDeckPreview(TrackMetadataUpdate update) {
          if (previewHotCache.remove(DeckReference.getDeckReference(update.player, 0)) != null) {
              deliverWaveformPreviewUpdate(update.player, null);
          }
      }
docs: We have received an update that invalidates the waveform preview for a player, so clear it 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 have no waveform preview for the associated player