code: private void flushHotCacheSlot(SlotReference slot) {
          // Iterate over a copy to avoid concurrent modification issues
          for (Map.Entry<DeckReference, TrackMetadata> entry : new HashMap<DeckReference,TrackMetadata>(hotCache).entrySet()) {
              if (slot == SlotReference.getSlotReference(entry.getValue().trackReference)) {
                  logger.debug("Evicting cached metadata in response to unmount report {}", entry.getValue());
                  hotCache.remove(entry.getKey());
              }
          }
      }
docs: Discards any tracks from the hot cache that were loaded from a now-unmounted media slot, because they are no
  longer valid.