RsId { public boolean isEmpty() { return id == EMPTY.id; } private  RsId(int id); static RsId of(int id); static RsId of(String id); static RsId empty(); int getId(); boolean isEmpty(); @Override int hashCode(); @Override boolean equals(Object o); @Override String toString();  }
@Test public void testIsEmpty() { assertThat(RsId.empty().isEmpty(), is(true)); }