public @Nullable V forcePut(K key, V value) {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.forcePut(key, value);
    }

    @Override
    public BiMap<V, K> inverse() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.inverse();
    }

    @Override
    public Set<V> values() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.values();
    }

      assertTrue(Thread.holdsLock(mutex));
      return delegate.forcePut(key, value);
    }

    @Override
    public BiMap<V, K> inverse() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.inverse();
    }

    @Override
    public void replaceAll(BiFunction<? super K, ? super V, ? extends V> function) {
      assertTrue(Thread.holdsLock(mutex));
      delegate.replaceAll(function);