assertNull(doc.get("title_ja")); // title is not in langFields
        assertNull(doc.get("content_ja")); // content is not in langFields
    }

    public void test_getSupportedLanguage_caseInsensitive() {
        // Test that method is case sensitive (as per implementation)
        assertNull(languageHelper.getSupportedLanguage("JA"));
        assertNull(languageHelper.getSupportedLanguage("EN"));