return delegate().containsEntry(key, value);
      }
    }

    @Override
    public Collection<V> get(@ParametricNullness K key) {
      synchronized (mutex) {
        return typePreservingCollection(delegate().get(key), mutex);
      }
    }

    @Override
    public boolean put(@ParametricNullness K key, @ParametricNullness V value) {
      synchronized (mutex) {

        return delegate().containsEntry(key, value);
      }
    }

    @Override
    public Collection<V> get(@ParametricNullness K key) {
      synchronized (mutex) {
        return typePreservingCollection(delegate().get(key), mutex);
      }
    }

    @Override
    public boolean put(@ParametricNullness K key, @ParametricNullness V value) {
      synchronized (mutex) {