Pray, what is the reason of that?'

    `In my youth,' said the sage, as he shook his grey locks,
      `I kept all my limbs very supple
    By the use of this ointment--one shilling the box--
      Allow me to sell you a couple?'

    `You are old,' said the youth, `and your jaws are too weak
      For anything tougher than suet;
    Yet you finished the goose, with the bones and the beak--

  }

  /** An implementation of {@link Map#putAll}. */
  static <K extends @Nullable Object, V extends @Nullable Object> void putAllImpl(
      Map<K, V> self, Map<? extends K, ? extends V> map) {
    for (Entry<? extends K, ? extends V> entry : map.entrySet()) {
      self.put(entry.getKey(), entry.getValue());
    }
  }

  static class KeySet<K extends @Nullable Object, V extends @Nullable Object>

      Pray, what is the reason of that?'

    `In my youth,' said the sage, as he shook his grey locks,
      `I kept all my limbs very supple
    By the use of this ointment--one shilling the box--
      Allow me to sell you a couple?'

    `You are old,' said the youth, `and your jaws are too weak
      For anything tougher than suet;
    Yet you finished the goose, with the bones and the beak--