WeakConcurrentMap extends ReferenceQueue<K> { @Nullable public V remove(K key) { if (key == null) throw new NullPointerException("key == null"); expungeStaleEntries(); return target.remove(key); }  @Nullable V getIfPresent(K key); @Nullable V putIfProbablyAbsent(K key, V value); @Nullable V remove(K key); @Override String toString();  }
@Test public void remove_okWhenDoesntExist() { map.remove(key); }