### Question:
OptionalClasses { OptionalClasses() { throw new UnsupportedOperationException(); } OptionalClasses();  static final Class<Annotation> SERVER_ENDPOINT; static final Class<?> ENTITY_MANAGER_FACTORY; static final Class<?> ENTITY_MANAGER; }### Answer:
@Test public void testOptionalClasses() { assertNotNull(OptionalClasses.ENTITY_MANAGER); assertNull(OptionalClasses.SERVER_ENDPOINT); }