@Test
    void verifyEmptyValue() {
        val names = new ArrayList();
        names.add(100);
        names.add(ArrayUtils.EMPTY_BYTE_ARRAY);

        val altNames = new HashSet();
        altNames.add(names);

        var results = X509UPNExtractorUtils.extractUPNString(altNames);
        assertTrue(results.isEmpty());

        results = X509UPNExtractorUtils.extractUPNString(List.of());
        assertTrue(results.isEmpty());

        results = X509UPNExtractorUtils.extractUPNString(List.of(List.of(100)));
        assertTrue(results.isEmpty());
    }
This is {@link X509UPNExtractorUtilsTests}.

@author Misagh Moayyed
@since 6.4.0
support/cas-server-support-x509-core/src/test/java/org/apereo/cas/adaptors/x509/authentication/principal/X509UPNExtractorUtilsTests.java