void (Map<String, ? super String> map) { UsefulTestCase.assertThrows(IllegalArgumentException.class, () -> map.put(null, "ab")); assertEquals(0, map.size()); UsefulTestCase.assertThrows(IllegalArgumentException.class, () -> map.get(null)); UsefulTestCase.assertThrows(IllegalArgumentException.class, () -> map.remove(null)); assertTrue(map.isEmpty()); }