code: @SuppressWarnings("WeakerAccess")
      public Map<DeckReference, WaveformPreview> getLoadedPreviews() {
          ensureRunning();
          // Make a copy so callers get an immutable snapshot of the current state.
          return Collections.unmodifiableMap(new HashMap<DeckReference, WaveformPreview>(previewHotCache));
      }
docs: Get the waveform previews available for all tracks currently loaded in any player, either on the play deck, or
  in a hot cue.
  
  @return the previews associated with all current players, including for any tracks loaded in their hot cue slots
  
  @throws IllegalStateException if the WaveformFinder is not running