@Override
    public E getLast() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.getLast();
    }

    @Override
    public @Nullable E peekFirst() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.peekFirst();
    }

    @Override
    public @Nullable E peekLast() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.peekLast();
    }

  @Override
  public boolean offerLast(@ParametricNullness E e) {
    return delegate().offerLast(e);
  }

  @Override
  public @Nullable E peekFirst() {
    return delegate().peekFirst();
  }

  @Override
  public @Nullable E peekLast() {
    return delegate().peekLast();
  }

  @CanIgnoreReturnValue // TODO(cpovirk): Consider removing this?
  @Override

    @Override
    public E getLast() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.getLast();
    }

    @Override
    public @Nullable E peekFirst() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.peekFirst();
    }

    @Override
    public @Nullable E peekLast() {
      assertTrue(Thread.holdsLock(mutex));
      return delegate.peekLast();
    }