} else {
                        final long interval = fessConfig.getThumbnailGeneratorIntervalAsInteger().longValue();
                        if (interval > 0) {
                            ThreadUtil.sleep(interval);
                        }
                    }
                } else {

     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     * @throws NumberFormatException When the property is not integer.
     */
    Integer getThumbnailGeneratorIntervalAsInteger();

    /**
     * Get the value for the key 'thumbnail.generator.targets'. <br>
     * The value is, e.g. all <br>
     * comment: Targets for thumbnail generator (e.g., all).