return null;
    }

    /**
     * Adds a feature to the extractor.
     *
     * @param key   the key of the feature
     * @param value the value of the feature
     */
    public void addFeature(final String key, final String value) {
        if (StringUtil.isBlank(key) || StringUtil.isBlank(value)) {
            throw new CrawlerSystemException("key or value is null.");
        }

        attributeMap.put(name, value);
    }

    /**
     * Adds a feature to the factory.
     * @param key The key of the feature.
     * @param value The value of the feature.
     */
    public void addFeature(final String key, final String value) {
        featureMap.put(key, value);
    }

    /**
     * Adds a field rule.
     * @param name The name of the field.

     * Adds a parser feature configuration.
     *
     * @param key the feature key
     * @param value the feature value
     * @throws CrawlerSystemException if key or value is null
     */
    public void addFeature(final String key, final String value) {
        if (StringUtil.isBlank(key) || StringUtil.isBlank(value)) {