@Nonnull
    @Override
    public Optional<MetadataMap> get(@Nonnull T id) {
        Objects.requireNonNull(id, "id");
        return Optional.ofNullable(this.cache.getIfPresent(id));
    }
A basic implementation of {@link MetadataRegistry} using a LoadingCache.

@param <T> the type
helper/src/main/java/me/lucko/helper/metadata/AbstractMetadataRegistry.java