// Invalid unwrap
            assertThrows(ClassCastException.class, () -> sid.unwrap(String.class));
        }

        @Test
        @DisplayName("isEmpty and isBlank edge cases")
        void testEmptyAndBlank() throws Exception {
            // No subauthorities
            SID s1 = new SID("S-1-5");
            assertTrue(s1.isEmpty());
            // isBlank will fail if sub_authority is null, so we skip that check for s1