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.");
        }

		class="org.codelibs.fess.crawler.extractor.impl.XmlExtractor" />
	<component name="htmlXpathExtractor"
		class="org.codelibs.fess.crawler.extractor.impl.HtmlXpathExtractor">
		<postConstruct name="addFeature">
			<arg>"http://xml.org/sax/features/namespaces"</arg>
			<arg>"false"</arg>
		</postConstruct>
	</component>
	<component name="emlExtractor"
		class="org.codelibs.fess.crawler.extractor.impl.EmlExtractor"/>