assertEquals("ja", doc.get("lang"));
        assertEquals("タイトル", doc.get("title_ja"));
        assertNull(doc.get("content_ja")); // content field was not present
    }

    public void test_getSupportedLanguage_withWhitespace() {
        // Test that whitespace is not trimmed (as per implementation)
        assertNull(languageHelper.getSupportedLanguage(" ja "));
        assertNull(languageHelper.getSupportedLanguage("ja "));