assertNull(languageHelper.detectLanguage(null));
        assertNull(languageHelper.detectLanguage(""));
        assertNull(languageHelper.detectLanguage("   "));
    }

    public void test_detectLanguage_withoutDetector() {
        // Without a real detector, this would cause NullPointerException
        try {
            languageHelper.detectLanguage("This is English text");

        if (language == null) {
            for (final String f : langFields) {
                if (doc.containsKey(f)) {
                    language = detectLanguage(DocumentUtil.getValue(doc, f, String.class));
                    if (language != null) {
                        if (logger.isDebugEnabled()) {
                            logger.debug("set {} to lang field", language);