/*
     * These gymnastics are a little confusing. Basically this class has neither legacy nor
     * non-legacy behavior; it just needs to let the behaviors of the backing converters shine
     * through (which might even differ from each other!). So, we override the correctedDo* methods,
     * after which the do* methods should never be reached.
     */

    @Override
    protected C doForward(A a) {
      throw new AssertionError();

            final String thumbnailField = fessConfig.getIndexFieldThumbnail();
            docList.stream().forEach(doc -> {
                if (!thumbnailManager.offer(doc)) {
                    if (logger.isDebugEnabled()) {
                        logger.debug("Removing {}={} from doc[{}]", thumbnailField, doc.get(thumbnailField),

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