code: public Set<MetadataProvider> getMetadataProviders(MediaDetails sourceMedia) {
          String key = (sourceMedia == null)? "" : sourceMedia.hashKey();
          Set<MetadataProvider> result = metadataProviders.get(key);
          if (result == null) {
              return Collections.emptySet();
          }
          return Collections.unmodifiableSet(new HashSet<MetadataProvider>(result));
      }
docs: Get the set of metadata providers that can offer metadata for tracks loaded from the specified media.
  
  @param sourceMedia the media whose metadata providers are desired, or {@code null} to get the set of
  metadata providers that can offer metadata for all media.
  
  @return any registered metadata providers that reported themselves as supporting tracks from that media