assertTrue(keySet.isEmpty());
    } else {
      assertThrows(UnsupportedOperationException.class, keySet::clear);
    }
    assertInvariants(map);
  }

  public void testKeySetRemoveAllNullFromEmpty() {
    Map<K, V> map;
    try {
      map = makeEmptyMap();
    } catch (UnsupportedOperationException e) {
      return;
    }

    Set<K> keySet = map.keySet();