void () { Iterable<Object> concat = ContainerUtil.concat(Collections.emptySet(), Collections.emptySet()); assertFalse(concat.iterator().hasNext()); Iterable<Object> foo = ContainerUtil.concat(Collections.emptySet(), Collections.singletonList("foo")); Iterator<Object> iterator = foo.iterator(); assertTrue(iterator.hasNext()); assertEquals("foo", iterator.next()); assertFalse(iterator.hasNext()); foo = ContainerUtil.concat(Collections.singletonList("foo"), Collections.emptySet()); iterator = foo.iterator(); assertTrue(iterator.hasNext()); assertEquals("foo", iterator.next()); assertFalse(iterator.hasNext()); foo = ContainerUtil.concat(Collections.singletonList("foo"), Collections.singleton("bar")); iterator = foo.iterator(); assertTrue(iterator.hasNext()); assertEquals("foo", iterator.next()); assertTrue(iterator.hasNext()); assertEquals("bar", iterator.next()); assertFalse(iterator.hasNext()); }